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)
 9 Months Ended
Dec. 31, 2017
$ / shares
shares
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Options Outstanding, Number of Shares (in shares) | shares 9,919,488
Options Exercisable, Number of Shares (in shares) | shares 5,065,645
$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 7,652
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 0.24
Options Outstanding, Weighted Average Remaining Life (Years) 2 years 2 months 23 days
Options Exercisable, Number of Shares (in shares) | shares 7,652
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 3,202,046
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 0.73
Options Outstanding, Weighted Average Remaining Life (Years) 8 years 9 months 25 days
Options Exercisable, Number of Shares (in shares) | shares 520,025
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 0.71
$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 2,832,305
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 1.27
Options Outstanding, Weighted Average Remaining Life (Years) 8 years 5 months
Options Exercisable, Number of Shares (in shares) | shares 1,215,155
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 1.31
$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 446,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 1.55
Options Outstanding, Weighted Average Remaining Life (Years) 8 years 11 months 13 days
Options Exercisable, Number of Shares (in shares) | shares 148,622
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 1.51
$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 253,779
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 2.43
Options Outstanding, Weighted Average Remaining Life (Years) 3 years 29 days
Options Exercisable, Number of Shares (in shares) | shares 220,445
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 2.42
$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 908,756
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 2.61
Options Outstanding, Weighted Average Remaining Life (Years) 6 years 2 months 10 days
Options Exercisable, Number of Shares (in shares) | shares 818,757
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 907,384
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 3.96
Options Outstanding, Weighted Average Remaining Life (Years) 5 years 9 months
Options Exercisable, Number of Shares (in shares) | shares 850,507
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 831,566
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 4.14
Options Outstanding, Weighted Average Remaining Life (Years) 5 years 5 months 13 days
Options Exercisable, Number of Shares (in shares) | shares 763,443
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 4.14
$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) 5 years 2 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 470,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 16.32
Options Outstanding, Weighted Average Remaining Life (Years) 1 year 4 days
Options Exercisable, Number of Shares (in shares) | shares 461,039
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 16.53