Equity-Based Compensation - Schedule of Activity Related to Stock Option Awards (Detail) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options, Outstanding, Beginning Balance | shares	2,923,448
Options, Forfeited | shares	(361,983)
Options, Expired | shares	(1,493,409)
Options, Exercised | shares	(64,590)
Options, Outstanding, Ending Balance | shares	1,003,466
Options, Exercisable at June 30, 2018 | shares	578,604
Weighted Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 18.78
Weighted Average Exercise Price, Forfeited | $ / shares	18.00
Weighted Average Exercise Price, Expired | $ / shares	19.46
Weighted Average Exercise Price, Exercised | $ / shares	18.34
Weighted Average Exercise Price, Outstanding, Ending Balance | $ / shares	18.07
Weighted Average Exercise Price, Exercisable at June 30, 2018 | $ / shares	$ 18.32
Weighted Average Remaining Contractual Life, Outstanding at June 30, 2018	7 years 3 months 21 days
Weighted Average Remaining Contractual Life, Exercisable at June 30, 2018	7 years 2 months 8 days
Aggregate Intrinsic Value, Outstanding at June 30, 2018 | $	$ 3,762
Aggregate Intrinsic Value, Exercisable at June 30, 2018 | $	$ 2,025