Share-Based Compensation (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Summary of stock option activity
Stock Options, Beginning balance	2,181,000
Stock option granted	0
Stock Options, Exercised	(121,000)
Stock option, Canceled	0
Stock Options, Ending balance	2,060,000
Stock Options, Exercisable	984,000
Stock Options, Vested and Expected to vest	2,032,000
Weighted-Average Exercise Price, Beginning balance	$ 17.20
Weighted-Average Exercise Price, Granted	$ 0.00
Weighted-Average Exercise Price, Exercised	$ 16.08
Weighted-Average Exercise Price, Canceled	$ 0.00
Weighted-Average Exercise Price, Ending balance	$ 17.27
Weighted-Average Exercise Price, Exercisable	$ 17.28
Weighted-Average Exercise Price, Vested and Expected to vest	$ 17.28
Summary of nonvested stock activity
Shares, Beginning balance	1,451,000
Shares, Granted	0
Shares, Vested	(7,000)
Shares, Forfeited/Canceled	0
Shares, Ending balance	1,444,000
Grant Date Weighted-Average Fair Value Per Share, Beginning balance	$ 19.90
Grant Date Weighted-Average Fair Value Per Share, Granted	$ 0.00
Grant Date Weighted-Average Fair Value Per Share, Vested	$ 22.98
Grant Date Weighted-Average Fair Value Per Share, Forfeited/Canceled	$ 0.00
Grant Date Weighted-Average Fair Value Per Share, Ending balance	$ 19.89
Nonvested Stock Awards [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 16,000,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	2 years 256 days
Allocated Share-based Compensation Expense	2,600,000	3,700,000
Summary of nonvested stock activity
Shares, Granted	0
Employee Stock Option [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	4,900,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	2 years 329 days
Allocated Share-based Compensation Expense	$ 604,000	$ 474,000