Stockholders' Equity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Summary of stock option activity
Number of Shares, Outstanding at December 31, 2012	1,936
Number of Shares, Granted	62
Number of Shares, Exercised	(45)
Number of Shares, Forfeited	(32)
Number of Shares, Outstanding at March 31, 2013	1,921
Number of Shares, Exercisable at March 31, 2013	1,071
Weighted Average Exercise Price Per Share, Outstanding, Beginning balance	$ 29.03
Weighted Average Exercise Price Per Share, Granted	$ 27.68
Weighted Average Exercise Price Per Share, Exercised	$ 18.61
Weighted Average Exercise Price Per Share, Forfeited	$ 30.75
Weighted Average Exercise Price Per Share, Outstanding, Ending balance	$ 29.20
Weighted Average Exercise Price Per Share, Exercisable at March 31, 2013	$ 26.88
Weighted Average Remaining Contractual Term, Outstanding at March 31, 2013	6 years 4 months 6 days
Weighted Average Remaining Contractual Term, Exercisable at March 31, 2013	4 years 8 months 9 days
Aggregate Intrinsic Value, Outstanding at March 31, 2013	$ 6,332
Aggregate Intrinsic Value, Exercisable at March 31, 2013	$ 5,346