Stock-based Compensation Stock-based Compensation (Details 5) (Stock Option Awards, USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Stock Option Awards
Shares
Outstanding, beginning of period (in shares)	6,642
Granted (in shares)	0
Exercised (in shares)	(92)
Forfeited (in shares)	(8)
Outstanding, end of period (in shares)	6,542	6,642
Exercisable, end of period (in shares)	5,640
Vested and expected to vest, end of period (in shares)	6,497
Weighted Average Exercise Price
Outstanding, beginning of period (in dollars per share)	$ 21.64
Granted (in dollars per share)	$ 0.00
Exercised (in dollars per share)	$ 12.93
Forfeited (in dollars per share)	$ 21.40
Outstanding, end of period (in dollars per share)	$ 21.77	$ 21.64
Exercisable, end of period (in dollars per share)	$ 20.94
Vested and expected to vest, end of period (in dollars per share)	$ 21.73
Weighted-Average Remaining Contractual Term (in years)
Outstanding, beginning of period (in years)	4 years 6 months	4 years 8 months
Outstanding, end of period (in years)	4 years 6 months	4 years 8 months
Exercisable, end of period (in years)	3 years 11 months
Vested and expected to vest, end of period (in years)	4 years 6 months
Aggregate Intrinsic Value
Outstanding, end of period	$ 38,402
Exercisable, end of period	36,535
Vested and expected to vest, end of period	$ 38,308