Stockholders' Equity - Additional Information (Detail) - USD ($)				1 Months Ended				3 Months Ended						6 Months Ended		9 Months Ended		12 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, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2014	Jun. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	May. 23, 2011
Class of Stock [Line Items]
Weighted average contractual term of awards outstanding																		1 year 5 months 5 days	1 year 4 months 28 days	2 years 6 months 22 days
Options vested																		0	0	0
Options granted										0				0		0		0	0	0
Cash received from option exercise under all share-based payment arrangements																		$ 10,100,000	$ 400,000	$ 800,000
Tax benefit from share based payment arrangement																		10,700,000	1,200,000	1,500,000
Aggregate intrinsic value of options exercised																		40,100,000	4,800,000	5,200,000
Aggregate intrinsic value of options outstanding																		3,000,000	44,000,000	23,700,000
Aggregate intrinsic value of options exercisable																		3,000,000	44,000,000	23,700,000
Value of common stock repurchased										$ 13,571,000				$ 13,971,000		$ 13,971,000		$ 19,179,000	$ 3,707,000	$ 1,195,000
1.50% Convertible Notes
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%	1.50%
Value of common stock repurchased	$ 69,000,000
2.50% Convertible Notes
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%		2.50%
Warrant
Class of Stock [Line Items]
Weighted average contractual term of awards outstanding and exercisable																		3 years 9 months 4 days	3 years 7 months 28 days	4 years 7 months 28 days
Exercised										85,000				140,000		140,000		170,000	0	0
Share based compensation awards granted in period										0				0		0		0	0	0
Stock Repurchase Program
Class of Stock [Line Items]
Repurchase of common stock authorized value					$ 300,000,000		$ 200,000,000
Period of common stock repurchase, years					3 years		3 years
Repurchase of common stock, available for repurchase								$ 47,500,000	$ 74,800,000	$ 109,700,000				$ 74,800,000		$ 47,500,000
2013 Program
Class of Stock [Line Items]
Repurchase of common stock authorized value						$ 300,000,000
Period of common stock repurchase, years						3 years
Repurchase of common stock, available for repurchase																		$ 25,700,000
2014 Program
Class of Stock [Line Items]
Repurchase of common stock authorized value				$ 500,000,000
Period of common stock repurchase, years				3 years
Repurchase of common stock, available for repurchase								$ 500,000,000	$ 500,000,000	$ 500,000,000				$ 500,000,000		$ 500,000,000		$ 500,000,000
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
Common stock reserved for issuance								2,327,860	2,330,868	2,542,393				2,330,868		2,327,860		2,327,704
Common shares available for issuance																		0
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
Stock Options
Class of Stock [Line Items]
Compensation expense related to stock grants								$ 0	$ 0	$ 0	$ 0	$ 0	$ 0			$ 0	$ 0	$ 0	$ 0	$ 0
Restricted Stock
Class of Stock [Line Items]
Compensation expense related to stock grants								6,500,000	5,700,000	$ 2,500,000	$ 4,600,000	6,000,000	1,900,000	$ 8,200,000	$ 7,900,000	$ 14,700,000	12,500,000	$ 18,500,000	$ 20,000,000	$ 11,500,000
Share based compensation awards granted in period										41,791				253,316		256,324		256,480	1,247,879	232,203
Share based compensation awards granted in period, fair market value																		$ 10,400,000	$ 31,600,000	$ 4,100,000
Compensation cost not yet recognized								$ 7,800,000	$ 9,600,000	$ 8,800,000				$ 9,600,000		$ 7,800,000		$ 6,200,000
Compensation cost not yet recognized, period for recognition								3 years	3 years	3 years								3 years
Value of common stock repurchased									$ 400,000			$ 300,000		$ 14,000,000	$ 2,400,000	$ 14,000,000	$ 2,700,000	$ 19,200,000	$ 3,700,000	$ 1,200,000
Restricted common stock, value of shares withheld										$ 13,600,000			$ 2,100,000
Restricted Stock | Maximum
Class of Stock [Line Items]
Share based compensation awards vesting period										5 years				5 years		5 years		5 years	5 years	5 years