Stockholders' Equity - Additional Information (Detail) (USD $)	6 Months Ended	0 Months Ended							1 Months Ended		6 Months Ended	1 Months Ended		6 Months Ended	0 Months Ended			0 Months Ended		3 Months Ended				6 Months Ended
	Jun. 30, 2014	Mar. 18, 2013 1.50% Convertible Notes	Jun. 30, 2014 1.50% Convertible Notes	Dec. 31, 2013 1.50% Convertible Notes	Mar. 18, 2013 1.50% Convertible Notes	Jun. 30, 2014 2.50% Convertible Notes	Dec. 31, 2013 2.50% Convertible Notes	May 23, 2011 2.50% Convertible Notes	Jul. 31, 2013 Stock Repurchase Program	Oct. 31, 2011 Stock Repurchase Program	Jun. 30, 2014 Stock Repurchase Program	Feb. 28, 2013 2013 Program	Feb. 28, 2014 2014 Program	Jun. 30, 2014 2014 Program	Aug. 13, 2009 Stock Incentive Plan 2009	Jun. 30, 2014 Stock Incentive Plan 2009	Aug. 13, 2009 Stock Incentive Plan 2009	Aug. 15, 2012 Amended and Restated Stock Incentive Plan 2009	Aug. 15, 2012 Amended and Restated Stock Incentive Plan 2009	Jun. 30, 2014 Stock Options	Jun. 30, 2013 Stock Options	Jun. 30, 2014 Restricted Stock	Jun. 30, 2013 Restricted Stock	Jun. 30, 2014 Restricted Stock	Jun. 30, 2013 Restricted Stock	Jun. 30, 2014 Restricted Stock Maximum
Class of Stock [Line Items]
Repurchase of common stock authorized value									$ 300,000,000	$ 200,000,000		$ 300,000,000	$ 500,000,000
Period of common stock repurchase, years									3 years	3 years		3 years	3 years
Repurchase of common stock, available for repurchase											74,800,000			500,000,000
Number of common stock shares authorized under Equity Incentive Plan																	3,000,000		7,000,000
Plan expiration date															Aug. 13, 2019			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																2,330,868
Compensation expense related to stock grants																				0	0	5,700,000	6,000,000	8,200,000	7,900,000
Debt instrument, interest rate, stated percentage			1.50%	1.50%	1.50%	2.50%	2.50%	2.50%
Share based compensation awards vesting period																										5 years
Compensation cost not yet recognized																						9,600,000		9,600,000
Compensation cost not yet recognized, period for recognition																						3 years
Value of common stock repurchased	$ 13,971,000	$ 69,000,000																				$ 400,000	$ 300,000	$ 14,000,000	$ 2,400,000