Stock-based Compensation Stock-based Compensation (Details 5) (Stock Option Awards, USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Stock Option Awards
Shares
Outstanding, beginning of period (in shares)	6,642
Granted (in shares)	1,030
Exercised (in shares)	(266)
Forfeited (in shares)	(8)
Outstanding, end of period (in shares)	7,398	6,642
Exercisable, end of period (in shares)	6,032
Vested and expected to vest, end of period (in shares)	7,329
Weighted Average Exercise Price
Outstanding, beginning of period (in dollars per share)	$ 21.64
Granted (in dollars per share)	$ 24.58
Exercised (in dollars per share)	$ 14.07
Forfeited (in dollars per share)	$ 21.40
Outstanding, end of period (in dollars per share)	$ 22.32	$ 21.64
Exercisable, end of period (in dollars per share)	$ 21.75
Vested and expected to vest, end of period (in dollars per share)	$ 22.30
Weighted-Average Remaining Contractual Term (in years)
Outstanding, beginning of period (in years)	4 years 11 months	4 years 8 months
Outstanding, end of period (in years)	4 years 11 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 11 months
Aggregate Intrinsic Value
Outstanding, end of period	$ 70,176
Exercisable, end of period	60,831
Vested and expected to vest, end of period	$ 69,709