Equity Offering - Additional Information (Detail) - ATM Program - USD ($)		3 Months Ended	32 Months Ended
	Apr. 25, 2019	Mar. 31, 2019	Mar. 31, 2019	Jul. 28, 2016
Stockholders Equity Note [Line Items]
Proceeds from sale of common stock under ATM program		$ 3,375,000
Cowen and Company LLC
Stockholders Equity Note [Line Items]
Aggregate offering price authorized				$ 75,000,000
Proceeds from sale of common stock under ATM program gross		3,453,000	$ 52,980,000
Proceeds from sale of common stock under ATM program		3,375,000	51,788,000
Commissions paid		$ 78,000	$ 1,192,000
Common Stock | Cowen and Company LLC
Stockholders Equity Note [Line Items]
Shares sold under ATM program		893,650	4,599,586
Average price per share		$ 3.86	$ 11.52
Subsequent Event | Cowen and Company LLC
Stockholders Equity Note [Line Items]
Proceeds from sale of common stock under ATM program gross	$ 1,259,000
Proceeds from sale of common stock under ATM program	1,231,000
Commissions paid	$ 28,000
Subsequent Event | Common Stock | Cowen and Company LLC
Stockholders Equity Note [Line Items]
Shares sold under ATM program	356,350
Average price per share	$ 3.53