Employee Stock Plans - Stock Option Activity Table (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares outstanding	3,008,520	3,120,266
Shares outstanding, weighted-average exercise price	$ 32.93	$ 30.61
Shares granted	473,580
Shares granted, weighted-average exercise price	$ 40.10
Shares exercised	(523,879)
Shares exercised, weighted-average exercise price	$ 25.52
Shares forfeited	(61,447)
Shares forfeited, weighted-average exercise price	$ 33.68
Shares exercisable	1,844,749
Shares exercisable, weighted-average exercise price	$ 32.16
Shares outstanding, weighted-average remaining contractual life	71
Shares exercisable, weighted-average remaining contractual life	54
Shares outstanding, aggregate intrinsic value	$ 16,935
Shares exercisable, aggregate intrinsic value	$ 11,195