Stockholders' Equity - Stock Options and Employee Stock Purchase Plan - Additional Information (Detail) - USD ($)		3 Months Ended		9 Months Ended
	Apr. 24, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Weighted-average remaining contractual term of options exercisable				5 years 1 month 7 days
Weighted-average remaining contractual term of options outstanding				5 years 1 month 7 days
Number of common stock shares approved under ESPP		18,691,478		18,691,478
Expected life of options		6 years	6 years	6 years	6 years
Inducement Award Agreements [Member] | CEO [Member]
Class Of Stock [Line Items]
Stock options granted	2,088,212
2016 Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Number of common stock shares approved under ESPP		1,500,000		1,500,000
Employee subscription rate		15.00%		15.00%
Number of shares per employee				10,000
Fair market value at discount				85.00%
Purchase period				6 months
Initial offering period				2016-09
Description of plan				Shares under the ESPP are purchased at 85 percent of the fair market value at the lower of (i) the closing price on the first trading day of the six-month purchase period or (ii) the closing price on the last trading day of the six-month purchase period.
Expected life of options		6 months	6 months	6 months	6 months
Shares remaining available for purchase under ESPP		1,372,960		1,372,960
2016 Employee Stock Purchase Plan [Member] | Maximum [Member]
Class Of Stock [Line Items]
Compensation amount per employee				$ 25,000
Stock options [Member] | Inducement Award Agreements [Member] | CEO [Member]
Class Of Stock [Line Items]
Period for vesting schedule over start date	4 years
Award vesting conditions				These stock options vest over a four-year period with a quarter vesting on the one year anniversary of the vesting commencement date.
Stock options [Member] | 2016 Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Number of common stock shares approved under ESPP		1,372,960		1,372,960