Equity-Based Compensation - Share Activity with Respect to Restricted Stock (Detail) - Restricted stock - $ / shares	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Number of Shares
Number of Shares, Issued and unvested as of beginning of period (in shares)	2,109,341	2,136,928	2,644,030	2,692,481	2,668,975	3,480,828	2,644,030	3,480,828	3,480,828
Number of Shares, Granted (in shares)		54,310	286,256		112,397	434,283
Number of Shares, Vested (in shares)	(8,500)	(81,897)	(625,646)	(16,201)	(81,391)	(657,317)
Number of Shares, Forfeited (in shares)			(167,712)		(7,500)	(588,819)
Number of Shares, Issued and unvested as of end of period (in shares)	2,100,841	2,109,341	2,136,928	2,676,280	2,692,481	2,668,975	2,100,841	2,676,280	2,644,030
Weighted Average Grant Date Fair Value Per Share
Weighted Average Grant Date Fair Value, Issued and unvested as of beginning of period (in dollars per share)	$ 14.39	$ 14.22	$ 14.15	$ 15.73	$ 15.93	$ 16.51	$ 14.15	$ 16.51	$ 16.51
Weighted Average Grant Date Fair Value, Granted (in dollars per share)		13.95	13.85		9.33	8.44
Weighted Average Grant Date Fair Value, Vested (in dollars per share)	13.66	9.66	15.30	11.56	13.33	18.75
Weighted Average Grant Date Fair Value, Forfeited (in dollars per share)			8.44		8.44	10.69
Weighted Average Grant Date Fair Value, Issued and unvested as of end of period (in dollars per share)	$ 14.40	$ 14.39	$ 14.22	$ 15.76	$ 15.73	$ 15.93	$ 14.40	$ 15.76	$ 14.15