Shareholders' Equity - Additional Information (Detail)	12 Months Ended	29 Months Ended
	Dec. 31, 2018 USD ($) Vote $ / shares shares	Dec. 31, 2018 USD ($) Vote $ / shares shares	Dec. 31, 2017 shares	Jul. 28, 2016 USD ($)
Stockholders Equity Note [Line Items]
Common stock votes per share | Vote	1	1
Preferred stock, shares authorized | shares	5,000	5,000	5,000
ATM Program
Stockholders Equity Note [Line Items]
Proceeds from sale of common stock under ATM program	$ 2,849,000
ATM Program | 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	2,914,000	$ 49,527,000
Proceeds from sale of common stock under ATM program	2,849,000	48,412,000
Commissions paid	$ 65,000	$ 1,114,000
ATM Program | Common Stock | Cowen and Company LLC
Stockholders Equity Note [Line Items]
Shares sold under ATM program | shares	300,227	3,705,936
Average price per share | $ / shares	$ 9.71	$ 13.36