Stockholders' Equity - Additional Information (Detail) (USD $)	3 Months Ended	0 Months Ended	1 Months Ended				0 Months Ended		3 Months Ended
	Mar. 31, 2015	Mar. 18, 2013	Jul. 31, 2013	Oct. 31, 2011	Feb. 28, 2013	Feb. 28, 2014	Aug. 13, 2009	Aug. 15, 2012	Mar. 31, 2014	Dec. 31, 2014	May 23, 2011
Class of Stock [Line Items]
Value of common stock repurchased	$ 10,000,000
1.50% Convertible Notes
Class of Stock [Line Items]
Debt instrument, interest rate, stated percentage	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%
Accounts Payable
Class of Stock [Line Items]
Accounts payable and accrued expenses	700,000
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
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	18,700,000
2014 Program
Class of Stock [Line Items]
Repurchase of common stock authorized value						500,000,000
Period of common stock repurchase, years						3 years
Accounts payable and accrued expenses	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	2,293,161
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
Restricted Stock
Class of Stock [Line Items]
Compensation expense related to stock grants	2,600,000								2,500,000
Compensation cost not yet recognized	4,900,000
Compensation cost not yet recognized, period for recognition	3 years
Value of common stock repurchased	10,000,000								13,600,000
Restricted Stock | Maximum
Class of Stock [Line Items]
Share based compensation awards vesting period	5 years
Stock Options
Class of Stock [Line Items]
Compensation expense related to stock grants	$ 0								$ 0