Stock-based Compensation - Summary of Stock Appreciation Rights (Detail) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2016 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	4,109,184
Number of Shares, Granted	0
Number of Shares, Exercised	(226,700)
Number of Shares, Outstanding, Ending Balance	3,882,484
Number of Shares, Exercisable	3,717,284
Number of Shares, Vested and expected to vest	3,882,484
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 5.22
Weighted-Average Exercise Price, Exercised | $ / shares	5.23
Weighted-Average Exercise Price, Outstanding, Ending Balance | $ / shares	5.25
Weighted-Average Exercise Price, Exercisable | $ / shares	5.23
Weighted-Average Exercise Price, Vested and expected to vest | $ / shares	$ 5.25
Weighted-Average Remaining Contractual Term, Outstanding	5 years 18 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 9 months 29 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	5 years 18 days
Aggregate Intrinsic Value, Outstanding, Ending balance | $	$ 20,475
Aggregate Intrinsic Value, Exercisable | $	19,877
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 20,475
Performance-Based Stock Appreciation Rights [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Outstanding, Beginning Balance	778,774
Number of Shares, Granted	0
Number of Shares, Exercised	(12,450)
Number of Shares, Forfeited or expired	(1,000)
Number of Shares, Outstanding, Ending Balance	765,324
Number of Shares, Exercisable	765,324
Number of Shares, Vested and expected to vest	765,324
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 6.33
Weighted-Average Exercise Price, Exercised | $ / shares	2.91
Weighted-Average Exercise Price, Forfeited or expired | $ / shares	5.65
Weighted-Average Exercise Price, Outstanding, Ending Balance | $ / shares	6.34
Weighted-Average Exercise Price, Exercisable | $ / shares	6.34
Weighted-Average Exercise Price, Vested and expected to vest | $ / shares	$ 6.34
Weighted-Average Remaining Contractual Term, Outstanding	3 years 10 months 10 days
Weighted-Average Remaining Contractual Term, Exercisable	3 years 10 months 10 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	3 years 10 months 10 days
Aggregate Intrinsic Value, Outstanding, Ending balance | $	$ 3,569
Aggregate Intrinsic Value, Exercisable | $	3,569
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 3,569