Equity-Based Compensation - Activity with Respect to SARs (Detail) - SARs - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of Shares, Issued and unvested, beginning of period (in shares)	307,514	479,656	548,482
Number of Shares, Granted (in shares)		25,000	1,500
Number of Shares, Exercised (in shares)	(939)	(191,205)	(68,638)
Number of Shares, Forfeited (in shares)		(5,937)	(1,688)
Number of Shares, Issued and unvested, end of period (in shares)	306,575	307,514	479,656
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Weighted Average Base Price [Roll Forward]
Weighted Average Base Price, Beginning of period (in dollars per share)	$ 11.28	$ 10.64	$ 10.62
Weighted Average Base Price, Granted (in dollars per share)		9.02	16.69
Weighted Average Base Price, Exercised (in dollars per share)	9.98	9.35	10.67
Weighted Average Base Price, Forfeited (in dollars per share)		12.15	9.35
Weighted Average Base Price, End of period (in dollars per share)	11.28	11.28	10.64
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Fair Value, Beginning of period (in dollars per share)	6.16	5.80	5.79
Weighted Average Fair Value, Granted (in dollars per share)		4.79	8.99
Weighted Average Fair Value, Exercised (in dollars per share)	5.33	5.07	5.79
Weighted Average Fair Value, Forfeited (in dollars per share)		6.63	4.95
Weighted Average Fair Value, End of period (in dollars per share)	$ 6.16	$ 6.16	$ 5.80
Number of shares issued (in shares)	171	60,219	11,261