Stockholders' Equity - Additional Information (Detail) - USD ($)				1 Months Ended				3 Months Ended		9 Months Ended		12 Months Ended				57 Months Ended
	Mar. 18, 2013	Aug. 15, 2012	Aug. 13, 2009	Feb. 28, 2014	Jul. 31, 2013	Feb. 28, 2013	Oct. 31, 2011	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2015	May 23, 2011
Class of Stock [Line Items]
Value of common stock repurchased										$ 12,391,000		$ 193,434,000	$ 436,419,000	$ 125,341,000	$ 19,138,000	$ 786,723,000
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018
Class of Stock [Line Items]
Debt instrument, interest rate, stated percentage	1.50%							1.50%	1.50%	1.50%	1.50%	1.50%				1.50%
Value of common stock repurchased	$ 69,000,000
Convertible Notes | 2.50% Senior Subordinated Notes Due June 2016
Class of Stock [Line Items]
Debt instrument, interest rate, stated percentage								2.50%	2.50%	2.50%	2.50%	2.50%				2.50%	2.50%
Stock Options
Class of Stock [Line Items]
Compensation expense related to stock grants								$ 0	$ 0	$ 0	$ 0
Restricted Stock
Class of Stock [Line Items]
Compensation expense related to stock grants								3,900,000	$ 6,500,000	9,800,000	14,700,000
Compensation cost not yet recognized								$ 2,600,000		$ 2,600,000						$ 2,600,000
Compensation cost not yet recognized, period for recognition										3 years
Value of common stock repurchased										$ 15,500,000	$ 13,700,000
Restricted Stock | Maximum
Class of Stock [Line Items]
Share based compensation awards vesting period										5 years
Stock Incentive Plan 2009
Class of Stock [Line Items]
Number of common stock shares authorized under Equity Incentive Plan			3,000,000
Plan expiration date			Aug. 13, 2019
Amended and Restated Stock Incentive Plan 2009
Class of Stock [Line Items]
Number of common stock shares authorized under Equity Incentive Plan		7,000,000
Plan expiration date		Aug. 15, 2022
Number of additional common stock shares approved for issuance under amended and restated 2009 Equity Incentive Plan		4,000,000
Common stock reserved for issuance								2,124,475		2,124,475						2,124,475
Previous Plan
Class of Stock [Line Items]
Common stock reserved for issuance								0		0						0
February 2013 Program
Class of Stock [Line Items]
Repurchase of common stock authorized value						$ 300,000,000
Period of common stock repurchase, years						3 years
2011 Program
Class of Stock [Line Items]
Repurchase of common stock authorized value							$ 200,000,000
Period of common stock repurchase, years							3 years
July 2013 Program
Class of Stock [Line Items]
Repurchase of common stock authorized value					$ 300,000,000
Period of common stock repurchase, years					3 years
Accounts payable and accrued expenses								$ 13,300,000		$ 13,300,000						$ 13,300,000
February 2014 Program
Class of Stock [Line Items]
Repurchase of common stock authorized value				$ 500,000,000
Period of common stock repurchase, years				3 years
Accounts payable and accrued expenses								$ 500,000,000		$ 500,000,000						$ 500,000,000