Stock-based Compensation - Summary of Stock Appreciation Rights (Detail) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Time-Based Stock Appreciation Rights [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Outstanding, Beginning Balance	2,564,394
Number of Shares, Granted	0
Number of Shares, Exercised	(57,000)
Number of Shares, Outstanding, Ending Balance	2,507,394
Number of Shares, Exercisable	2,447,394
Number of Shares, Vested and expected to vest	2,507,394
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 5.38
Weighted-Average Exercise Price, Exercised | $ / shares	5.28
Weighted-Average Exercise Price, Outstanding, Ending Balance | $ / shares	5.32
Weighted-Average Exercise Price, Exercisable | $ / shares	5.35
Weighted-Average Exercise Price, Vested and expected to vest | $ / shares	$ 5.32
Weighted-Average Remaining Contractual Term, Outstanding	4 years 7 months 6 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 5 months 26 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	4 years 7 months 6 days
Aggregate Intrinsic Value, Outstanding, Ending balance | $	$ 9,173
Aggregate Intrinsic Value, Exercisable | $	9,574
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 9,173
Performance-Based Stock Appreciation Rights [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Outstanding, Beginning Balance	504,473
Number of Shares, Granted	0
Number of Shares, Exercised	(8,100)
Number of Shares, Outstanding, Ending Balance	496,373
Number of Shares, Exercisable	496,373
Number of Shares, Vested and expected to vest	496,373
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 5.80
Weighted-Average Exercise Price, Exercised | $ / shares	2.58
Weighted-Average Exercise Price, Outstanding, Ending Balance | $ / shares	5.75
Weighted-Average Exercise Price, Exercisable | $ / shares	5.75
Weighted-Average Exercise Price, Vested and expected to vest | $ / shares	$ 5.75
Weighted-Average Remaining Contractual Term, Outstanding	3 years 5 months 8 days
Weighted-Average Remaining Contractual Term, Exercisable	3 years 5 months 8 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	3 years 5 months 8 days
Aggregate Intrinsic Value, Outstanding, Ending balance | $	$ 2,921
Aggregate Intrinsic Value, Exercisable | $	2,921
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 2,921