Equity-Based Compensation - Changes in Restricted Stock (Detail) - $ / shares	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value, Forfeited	$ 4.90			$ 5.44
Shares surrendered by employees for withholding taxes	3,330,000	26,032,000	207,649,000	2,239,000	21,523,000	46,039,000	237,011,000	69,801,000
Restricted Stock
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	3,586,023	3,508,624	3,755,275	3,811,935	3,738,582	1,185,071	3,755,275	1,185,071	1,185,071
Number of shares, granted	0	140,416	441,256	9,000	135,000	3,095,948
Number of shares, vested	(28,461)	(63,017)	(644,247)	(8,326)	(61,647)	(175,771)
Number of Shares, Forfeited	(26,125)		(43,660)	(1,875)		(366,666)
Number of shares, issued and unvested end of period	3,531,437	3,586,023	3,508,624	3,810,734	3,811,935	3,738,582	3,531,437	3,810,734	3,755,275
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted average grant date fair value, issued and unvested beginning balance	$ 15.74	$ 15.75	$ 15.94	$ 15.84	$ 15.70	$ 9.52	$ 15.94	$ 9.52	$ 9.52
Weighted average fair value, granted	0.00	13.17	16.21	17.31	17.41	17.21
Weighted Average Grant Date Fair Value, Vested	14.27	10.80	19.70	9.25	10.52	12.68
Weighted Average Grant Date Fair Value, Forfeited	16.58		17.85	10.22		9.96
Weighted average grant date fair value, issued and unvested ending balance	$ 15.74	$ 15.74	$ 15.75	$ 15.86	$ 15.84	$ 15.70	$ 15.74	$ 15.86	$ 15.94