Annual report pursuant to Section 13 and 15(d)

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

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Description of Stock Plans - Exercise Price for Options Outstanding and Options Exercisable (Detail)
 12 Months Ended
Mar. 31, 2018
$ / shares
shares
Employee Stock Ownership Plan E S O P Disclosures [Line Items]  
Options Outstanding (in shares) | shares 9,741,969
Options Exercisable (in shares) | shares 4,729,348
$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 (in shares) | shares 6,204
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 0.24
Weighted-Average Remaining Life (Years) 1 year 11 months 28 days
Options Exercisable (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 (in shares) | shares 3,142,319
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 0.73
Weighted-Average Remaining Life (Years) 8 years 7 months 10 days
Options Exercisable (in shares) | shares 593,935
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 0.72
$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 (in shares) | shares 2,782,291
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 1.27
Weighted-Average Remaining Life (Years) 8 years 3 months 5 days
Options Exercisable (in shares) | shares 1,317,935
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 1.30
$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 (in shares) | shares 444,333
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 1.55
Weighted-Average Remaining Life (Years) 8 years 8 months 13 days
Options Exercisable (in shares) | shares 177,618
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 1.52
$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 (in shares) | shares 716,822
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 2.22
Weighted-Average Remaining Life (Years) 9 years 6 months 17 days
Options Exercisable (in shares) | shares 93,456
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 (in shares) | shares 853,200
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 2.61
Weighted-Average Remaining Life (Years) 6 years 4 months 4 days
Options Exercisable (in shares) | shares 787,451
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 (in shares) | shares 765,300
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 3.96
Weighted-Average Remaining Life (Years) 6 years 6 months 10 days
Options Exercisable (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 (in shares) | shares 661,500
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 4.15
Weighted-Average Remaining Life (Years) 6 years 7 months 4 days
Options Exercisable (in shares) | shares 622,251
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 (in shares) | shares 60,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 4.65
Weighted-Average Remaining Life (Years) 4 years 11 months 27 days
Options Exercisable (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 (in shares) | shares 310,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 12.48
Weighted-Average Remaining Life (Years) 1 year 2 months 20 days
Options Exercisable (in shares) | shares 303,750
Options Exercisable, Weighted Average Exercise Price (in dollars per share) $ 12.62