Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended	32 Months Ended
	Apr. 25, 2019	Apr. 01, 2019	Mar. 31, 2019	Mar. 31, 2019
ATM Program
Subsequent Event [Line Items]
Proceeds from sale of common stock under ATM program			$ 3,375
ATM Program | Cowen and Company LLC
Subsequent Event [Line Items]
Proceeds from sale of common stock under ATM program gross			3,453	$ 52,980
Proceeds from sale of common stock under ATM program			3,375	51,788
Commissions paid			$ 78	$ 1,192
ATM Program | Common Stock | Cowen and Company LLC
Subsequent Event [Line Items]
Shares sold under ATM program			893,650	4,599,586
Average price per share			$ 3.86	$ 11.52
ATM Program | Subsequent Event | Cowen and Company LLC
Subsequent Event [Line Items]
Proceeds from sale of common stock under ATM program gross	$ 1,259
Proceeds from sale of common stock under ATM program	1,231
Commissions paid	$ 28
ATM Program | Subsequent Event | Common Stock | Cowen and Company LLC
Subsequent Event [Line Items]
Shares sold under ATM program	356,350
Average price per share	$ 3.53
Unsecured Promissory Notes | Subsequent Event
Subsequent Event [Line Items]
Repayments of Debt		$ 27,040