Stock-Based Compensation - Summary of Stock Appreciation Rights (Detail) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 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	(105,200)
Number of Shares, Forfeited or expired	(20,000)
Number of Shares, Outstanding, Ending Balance	2,439,194
Number of Shares, Exercisable	2,379,194
Number of Shares, Vested and expected to vest	2,439,194
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 5.38
Weighted-Average Exercise Price, Exercised | $ / shares	5.15
Weighted-Average Exercise Price, Forfeited or expired | $ / shares	8.58
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 3 months 14 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 2 months 4 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	4 years 3 months 14 days
Aggregate Intrinsic Value, Outstanding, Ending balance | $	$ 10,678
Aggregate Intrinsic Value, Exercisable | $	11,128
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 10,678
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	(10,500)
Number of Shares, Outstanding, Ending Balance	493,973
Number of Shares, Exercisable	493,973
Number of Shares, Vested and expected to vest	493,973
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 5.80
Weighted-Average Exercise Price, Exercised | $ / shares	3.02
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 2 months 1 day
Weighted-Average Remaining Contractual Term, Exercisable	3 years 2 months 1 day
Weighted-Average Remaining Contractual Term, Vested and expected to vest	3 years 2 months 1 day
Aggregate Intrinsic Value, Outstanding, Ending balance | $	$ 3,257
Aggregate Intrinsic Value, Exercisable | $	3,257
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 3,257