Stockholders' Equity - Summary of RSUs Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Weighted Average Grant Date Fair Value
Increase in treasury shares (in shares)	103,000	76,000
RSUs
Number of RSUs
Outstanding, beginning of year (in shares)	3,363,946	2,167,212
Granted (in shares)	2,001,642	2,341,168
Canceled (in shares)	(1,914,319)	(598,650)
Vested (in shares)	(713,916)	(545,784)
Outstanding, end of year (in shares)	2,737,353	3,363,946
Weighted Average Grant Date Fair Value
Outstanding, beginning of year (in dollars per share)	$ 2.78	$ 4.24
Granted (in dollars per share)	4.35	2.36
Canceled (in dollars per share)	2.75	4.75
Vested (in dollars per share)	3.61	4.59
Outstanding, end of year (in dollars per share)	$ 3.83	$ 2.78
RSUs | Chief Executive Officer
Number of RSUs
Granted (in shares)	535,000
RSUs, Excluding Performance-based
Number of RSUs
Granted (in shares)	2,001,642	789,167
Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 4.35	$ 2.38
Performance-based Restricted Stock Units
Number of RSUs
Granted (in shares)	0	1,552,001
Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 0.00	$ 2.35