Stock-Based Compensation Plans (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock option activity
Number of Shares, Beginning balance	2,927,737	4,403,562	5,166,558
Number of Shares, Granted	13,292	340,771	8,239
Number of Shares, Cancelled		(211,323)	(12,575)
Number of Shares, Exercised	(1,511,207)	(1,605,273)	(758,660)
Number of Shares, Ending Balance	1,429,822	2,927,737	4,403,562
Number of Shares, Exercisable	1,214,099
Weighted Average Exercise Price, Beginning Balance	$ 9.42	$ 9.09	$ 9.10
Weighted Average Exercise Price, Granted	$ 32.45	$ 21.60	$ 14.10
Weighted Average Exercise Price, Canceled		$ 16.16	$ 13.85
Weighted Average Exercise Price, Exercised	$ 5.64	$ 10.21	$ 9.17
Weighted Average Exercise Price, Ending Balance	$ 13.62	$ 9.42	$ 9.09
Weighted Average Exercise Price, Exercisable	$ 12.10
Remaining contractual term, Beginning balance	4 years 6 months	8 years 1 month 6 days
Remaining contractual term, Ending balance	4 years 6 months	8 years 1 month 6 days
Remaining contractual term, Exercisable	4 years
Intrinsic Value, Exercised	$ 41,310
Intrinsic Value, Ending balance	31,002
Intrinsic Value, Exercisable	$ 28,172