Stockholders' Equity - Additional Information (Detail) (USD $)	6 Months Ended		1 Months Ended				1 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Oct. 31, 2011 Stock Repurchase Program	Feb. 15, 2013 2013 Program	Aug. 13, 2009 Stock Incentive Plan 2009	Jun. 30, 2013 Stock Incentive Plan 2009	Aug. 15, 2012 Amended and Restated Stock Incentive Plan 2009	Jun. 30, 2013 Restricted Stock	Jun. 30, 2012 Restricted Stock	Jun. 30, 2013 Restricted Stock	Jun. 30, 2012 Restricted Stock	Jun. 30, 2013 Performance Shares
Class of Stock [Line Items]
Repurchase of common stock authorized value			$ 200,000,000	$ 300,000,000
Period of common stock repurchase, years			3 years	3 years
Repurchase of common stock, shares	11,900,000	5,200,000
Repurchase of common stock, value	302,764,000	85,100,000
Repurchase of common stock, available for repurchase	52,800,000
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						3,524,899
Compensation expense related to stock grants								6,000,000	2,600,000	7,900,000	5,200,000	3,000,000
Compensation cost not yet recognized								16,100,000		16,100,000
Compensation cost not yet recognized, period for recognition								3 years
Restricted common stock, value of shares withheld								$ 300,000	$ 300,000	$ 2,400,000	$ 400,000