Description of Stock Plans - Exercise Price for Options Outstanding and Options Exercisable (Detail)
 6 Months Ended
Sep. 30, 2016
$ / shares
shares
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Options Outstanding, Number of Shares (in shares) | shares 7,982,403
Options Exercisable, Number of Shares (in shares) | shares 3,498,410
$0.00 - 0.50  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of Exercise Price, lower limit $ 0
Range of Exercise Price, upper limit $ 0.50
Options Outstanding, Number of Shares (in shares) | shares 8,065
Options Outstanding, Weighted Average Exercise Price (in usd per share) $ 0.24
Options Outstanding, Weighted Average Remaining Life (Years) 3 years 5 months 23 days
Options Exercisable, Number of Shares (in shares) | shares 8,065
Options Exercisable, Weighted Average Exercise Price (in usd 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 0.51
Range of Exercise Price, upper limit $ 1.00
Options Outstanding, Number of Shares (in shares) | shares 159,923
Options Outstanding, Weighted Average Exercise Price (in usd per share) $ 0.70
Options Outstanding, Weighted Average Remaining Life (Years) 6 years 6 months
Options Exercisable, Number of Shares (in shares) | shares 136,136
Options Exercisable, Weighted Average Exercise Price (in usd per share) $ 0.65
$1.01 - 1.50  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of Exercise Price, lower limit 1.01
Range of Exercise Price, upper limit $ 1.5
Options Outstanding, Number of Shares (in shares) | shares 2,852,559
Options Outstanding, Weighted Average Exercise Price (in usd per share) $ 1.29
Options Outstanding, Weighted Average Remaining Life (Years) 2 years 11 months 16 days
Options Exercisable, Number of Shares (in shares) | shares 165,056
Options Exercisable, Weighted Average Exercise Price (in usd per share) $ 1.26
$1.51 - 2.00  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of Exercise Price, lower limit 1.51
Range of Exercise Price, upper limit $ 2
Options Outstanding, Number of Shares (in shares) | shares 316,055
Options Outstanding, Weighted Average Exercise Price (in usd per share) $ 1.51
Options Outstanding, Weighted Average Remaining Life (Years) 9 years 1 month 6 days
Options Exercisable, Number of Shares (in shares) | shares 74,250
Options Exercisable, Weighted Average Exercise Price (in usd 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 2.01
Range of Exercise Price, upper limit $ 2.50
Options Outstanding, Number of Shares (in shares) | shares 253,776
Options Outstanding, Weighted Average Exercise Price (in usd per share) $ 2.43
Options Outstanding, Weighted Average Remaining Life (Years) 4 years 3 months 29 days
Options Exercisable, Number of Shares (in shares) | shares 187,109
Options Exercisable, Weighted Average Exercise Price (in usd per share) $ 2.41
$2.51 - 3.00  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of Exercise Price, lower limit 2.51
Range of Exercise Price, upper limit $ 3.00
Options Outstanding, Number of Shares (in shares) | shares 1,162,456
Options Outstanding, Weighted Average Exercise Price (in usd per share) $ 2.62
Options Outstanding, Weighted Average Remaining Life (Years) 8 years 4 days
Options Exercisable, Number of Shares (in shares) | shares 657,341
Options Exercisable, Weighted Average Exercise Price (in usd 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 3.51
Range of Exercise Price, upper limit $ 4.00
Options Outstanding, Number of Shares (in shares) | shares 1,332,314
Options Outstanding, Weighted Average Exercise Price (in usd per share) $ 3.95
Options Outstanding, Weighted Average Remaining Life (Years) 8 years 2 months 5 days
Options Exercisable, Number of Shares (in shares) | shares 780,976
Options Exercisable, Weighted Average Exercise Price (in usd per share) $ 3.95
$4.01 - 4.50  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of Exercise Price, lower limit 4.01
Range of Exercise Price, upper limit $ 4.50
Options Outstanding, Number of Shares (in shares) | shares 1,367,255
Options Outstanding, Weighted Average Exercise Price (in usd per share) $ 4.20
Options Outstanding, Weighted Average Remaining Life (Years) 7 years 29 days
Options Exercisable, Number of Shares (in shares) | shares 984,477
Options Exercisable, Weighted Average Exercise Price (in usd per share) $ 4.22
$4.51 - 5.00  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Range of Exercise Price, lower limit 4.51
Range of Exercise Price, upper limit $ 5.00
Options Outstanding, Number of Shares (in shares) | shares 60,000
Options Outstanding, Weighted Average Exercise Price (in usd per share) $ 4.65
Options Outstanding, Weighted Average Remaining Life (Years) 6 years 5 months 27 days
Options Exercisable, Number of Shares (in shares) | shares 60,000
Options Exercisable, Weighted Average Exercise Price (in usd per share) $ 4.65
$5.01 and over  
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Exercise Price $ 5.01
Options Outstanding, Number of Shares (in shares) | shares 470,000
Options Outstanding, Weighted Average Exercise Price (in usd per share) $ 16.32
Options Outstanding, Weighted Average Remaining Life (Years) 2 years 3 months 4 days
Options Exercisable, Number of Shares (in shares) | shares 445,000
Options Exercisable, Weighted Average Exercise Price (in usd per share) $ 16.90