Summary of Significant Accounting Policies - Reconciliation of Basic and Diluted Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share Basic And Diluted [Abstract]
Net income	$ 6,913	$ 2,215	$ 4,840	$ (1,807)	$ 12,740	$ 157,014	$ 3,326	$ 2,618	$ 12,161	$ 175,698	$ 20,405
Denominator:
Weighted average common shares outstanding, basic									89,115,997	90,272,257	89,340,589
Basic earnings per share:
Net income per share	$ 0.08	$ 0.02	$ 0.05	$ (0.02)	$ 0.14	$ 1.73	$ 0.04	$ 0.03	$ 0.14	$ 1.95	$ 0.23
Denominator:
Weighted average common shares outstanding, basic									89,115,997	90,272,257	89,340,589
Dilutive securities:
Stock options									629,933	906,519	1,373,733
Restricted stock units									582,653	713,181	588,734
Weighted average common shares outstanding, diluted									90,328,583	91,891,957	91,303,056
Diluted earnings per share:
Net income per share	$ 0.08	$ 0.02	$ 0.05	$ (0.02)	$ 0.14	$ 1.70	$ 0.04	$ 0.03	$ 0.13	$ 1.91	$ 0.22