Fair Value Measurements - Schedule of Assets and Liabilities Carried at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Assets:
Cash equivalents	$ 47,089	$ 32,589
Derivative liabilities:
Warrants	3,875	1,217
Reported value measurement | Quoted Prices in Active Markets (Level 1)
Assets:
Cash equivalents	47,089	32,589
Reported value measurement | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0	0
Reported value measurement | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Warrants
Derivative liabilities:
Warrants	3,875	1,217	$ 455	$ 1,923
Warrants | Reported value measurement | Quoted Prices in Active Markets (Level 1)
Derivative liabilities:
Warrants	0	0
Warrants | Reported value measurement | Significant Other Observable Inputs (Level 2)
Derivative liabilities:
Warrants	0	0
Warrants | Reported value measurement | Significant Unobservable Inputs (Level 3)
Derivative liabilities:
Warrants	$ 3,875	$ 1,217