Quarterly report pursuant to Section 13 or 15(d)

Description of Stock Plans - Exercise Price for Options Outstanding and Options Exercisable (Details)

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Description of Stock Plans - Exercise Price for Options Outstanding and Options Exercisable (Details)
 3 Months Ended
Jun. 30, 2018
$ / shares
shares
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Options Outstanding, Number of Shares (in shares) | shares 10,401,823
Options Exercisable, Number of Shares (in shares) | shares 4,642,180
$0.00 - 0.50  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of exercise price, lower limit (in dollars per share) $ 0
Range of exercise price, upper limit (in dollars per share) $ 0.50
Options Outstanding, Number of Shares (in shares) | shares 6,618
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 0.24
Options Outstanding, Weighted Average Remaining Life (Years) 1 year 8 months 28 days
Options Exercisable, Number of Shares (in shares) | shares 6,618
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 0.24
$0.51 - 1.00  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of exercise price, lower limit (in dollars per share) 0.51
Range of exercise price, upper limit (in dollars per share) $ 1.00
Options Outstanding, Number of Shares (in shares) | shares 2,971,934
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 0.73
Options Outstanding, Weighted Average Remaining Life (Years) 8 years 4 months 10 days
Options Exercisable, Number of Shares (in shares) | shares 555,511
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 0.74
$1.01 - 1.50  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of exercise price, lower limit (in dollars per share) 1.01
Range of exercise price, upper limit (in dollars per share) $ 1.5
Options Outstanding, Number of Shares (in shares) | shares 2,737,634
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 1.28
Options Outstanding, Weighted Average Remaining Life (Years) 7 years 11 months 20 days
Options Exercisable, Number of Shares (in shares) | shares 1,421,057
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 1.29
$1.51 - 2.00  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of exercise price, lower limit (in dollars per share) 1.51
Range of exercise price, upper limit (in dollars per share) $ 2
Options Outstanding, Number of Shares (in shares) | shares 1,586,370
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 1.65
Options Outstanding, Weighted Average Remaining Life (Years) 9 years 6 months 7 days
Options Exercisable, Number of Shares (in shares) | shares 197,055
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 1.53
$2.01 - 2.50  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of exercise price, lower limit (in dollars per share) 2.01
Range of exercise price, upper limit (in dollars per share) $ 2.50
Options Outstanding, Number of Shares (in shares) | shares 709,267
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 2.22
Options Outstanding, Weighted Average Remaining Life (Years) 9 years 3 months 14 days
Options Exercisable, Number of Shares (in shares) | shares 122,735
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 2.33
$2.51 - 3.00  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of exercise price, lower limit (in dollars per share) 2.51
Range of exercise price, upper limit (in dollars per share) $ 3.00
Options Outstanding, Number of Shares (in shares) | shares 853,200
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 2.61
Options Outstanding, Weighted Average Remaining Life (Years) 6 years 1 month 3 days
Options Exercisable, Number of Shares (in shares) | shares 809,696
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 2.62
$3.51 - 4.00  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of exercise price, lower limit (in dollars per share) 3.51
Range of exercise price, upper limit (in dollars per share) $ 4.00
Options Outstanding, Number of Shares (in shares) | shares 765,300
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 3.96
Options Outstanding, Weighted Average Remaining Life (Years) 6 years 2 months 19 days
Options Exercisable, Number of Shares (in shares) | shares 765,300
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 3.96
$4.01 - 4.50  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of exercise price, lower limit (in dollars per share) 4.01
Range of exercise price, upper limit (in dollars per share) $ 4.50
Options Outstanding, Number of Shares (in shares) | shares 661,500
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 4.15
Options Outstanding, Weighted Average Remaining Life (Years) 6 years 1 month 28 days
Options Exercisable, Number of Shares (in shares) | shares 657,333
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 4.15
$4.51 - 5.00  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of exercise price, lower limit (in dollars per share) 4.51
Range of exercise price, upper limit (in dollars per share) $ 5.00
Options Outstanding, Number of Shares (in shares) | shares 60,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 4.65
Options Outstanding, Weighted Average Remaining Life (Years) 4 years 8 months 27 days
Options Exercisable, Number of Shares (in shares) | shares 60,000
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 4.65
$5.01 and over  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Exercise price (in dollars per share) $ 5.01
Options Outstanding, Number of Shares (in shares) | shares 50,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 5.89
Options Outstanding, Weighted Average Remaining Life (Years) 6 years 2 months 12 days
Options Exercisable, Number of Shares (in shares) | shares 46,875
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 5.89