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)
 6 Months Ended
Sep. 30, 2018
$ / shares
shares
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Options Outstanding, Number of Shares (in shares) | shares 9,756,330
Options Exercisable, Number of Shares (in shares) | shares 4,836,214
$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 6,204
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 0.24
Options Outstanding, Weighted Average Remaining Life (Years) 1 year 5 months 23 days
Options Exercisable, Number of Shares (in shares) | shares 6,204
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 2,696,614
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 0.73
Options Outstanding, Weighted Average Remaining Life (Years) 8 years 29 days
Options Exercisable, Number of Shares (in shares) | shares 582,288
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 0.75
$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 2,567,615
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 1.28
Options Outstanding, Weighted Average Remaining Life (Years) 7 years 8 months 5 days
Options Exercisable, Number of Shares (in shares) | shares 1,517,113
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 1.28
$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 1,534,339
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 1.65
Options Outstanding, Weighted Average Remaining Life (Years) 9 years 2 months 23 days
Options Exercisable, Number of Shares (in shares) | shares 309,398
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 1.58
$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 597,766
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 2.18
Options Outstanding, Weighted Average Remaining Life (Years) 9 years 4 months 13 days
Options Exercisable, Number of Shares (in shares) | shares 67,419
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 2.04
$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 827,992
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 2.61
Options Outstanding, Weighted Average Remaining Life (Years) 5 years 7 months 17 days
Options Exercisable, Number of Shares (in shares) | shares 827,992
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 2.61
$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 757,800
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 3.96
Options Outstanding, Weighted Average Remaining Life (Years) 5 years 10 months 2 days
Options Exercisable, Number of Shares (in shares) | shares 757,800
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 658,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 4.15
Options Outstanding, Weighted Average Remaining Life (Years) 5 years 6 months 11 days
Options Exercisable, Number of Shares (in shares) | shares 658,000
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 5 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) 5 years 11 months 12 days
Options Exercisable, Number of Shares (in shares) | shares 50,000
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 5.89