Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Nov. 30, 2010	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	May 05, 2016
Stockholders Equity Note [Line Items]
Proceeds from common stock sold		$ 22,121,000	$ 75,300,000	$ 18,488,000
Preferred stock, shares issued		0	0
Class of warrants outstanding		0
2010 Warrants
Stockholders Equity Note [Line Items]
Warrants, number of common stock shares	3,700,000
Warrant exercise price	$ 3.20
Warrants exercisable date	May 15, 2011
Exercisable period	5 years
Class of warrants outstanding		0
Stockholder Rights Plan
Stockholders Equity Note [Line Items]
Minimum percentage of common stock acquired by stockholders		15.00%
Designated preferred stock for future issuance		250,000
Series C Junior Participating preferred stock
Stockholders Equity Note [Line Items]
Preferred stock, shares issued		0
Cantor | Sales Agreement | Amendment No. 2
Stockholders Equity Note [Line Items]
Maximum common stock offering price		$ 132,200,000
Common stock registered for sale		$ 62,300,000			$ 70,000,000
Percentage of proceeds payable as compensation to underwriter		2.00%
Common stock, number of shares issued		3,500,000	0
Proceeds from common stock sold		$ 22,000,000	$ 0