Equity-Based Compensation - Activity related to DSUs (Detail) - Non-Management Director Compensation Plan (the Director Plan) - Deferred Stock Units - $ / 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)	22,500	28,125	33,750	45,000	90,000	90,000	33,750	90,000	90,000
Number of Shares, Activity for the three months ended (in shares)						0
Number of Shares, Vested (in shares)	(5,625)	(5,625)	(5,625)	(5,625)	(30,000)
Number of Shares, Forfeited (in shares)					(15,000)
Number of Shares, Issued and unvested as of end of period (in shares)	16,875	22,500	28,125	39,375	45,000	90,000	16,875	39,375	33,750
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)	$ 13.17	$ 13.17	$ 13.17	$ 13.17	$ 13.17	$ 13.17	$ 13.17	$ 13.17	$ 13.17
Weighted Average Grant Date Fair Value, Activity for the three months ended March 31, 2016 (in dollars per share)						0.00
Weighted Average Grant Date Fair Value, Vested (in dollars per share)	13.17	13.17	13.17	13.17	13.17
Weighted Average Grant Date Fair Value, Forfeited (in dollars per share)					13.17
Weighted Average Grant Date Fair Value, Issued and unvested as of end of period (in dollars per share)	$ 13.17	$ 13.17	$ 13.17	$ 13.17	$ 13.17	$ 13.17	$ 13.17	$ 13.17	$ 13.17