Compensation Plans Employee Stock Purchase Plan (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Compensation plans
Number of shares available for grant	3,800,000
Proceeds from sale of common stock	$ 6,858,000	$ 5,816,000	$ 7,327,000
Stock-based compensation expense	32,347,000	30,185,000	26,824,000
Employee Stock [Member]
Compensation plans
Maximum employee subscription rate	15.00%
Maximum employee subscription	25,000
Percent of offering date price paid	85.00%
Number of shares available for grant	1,200,000
Issuance of common stock under Employee Stock Purchase Plan (in shares)	77,427	66,485	41,358
Proceeds from sale of common stock	3,700,000	2,800,000	2,300,000
Risk free interest rate	0.10%	0.10%	0.20%
Dividend yield	0.20%	0.20%	0.20%
Volatility factor of the expected market price of the Company's common stock	41.10%	47.80%	36.30%
Expected life (in years)	6 months	6 months	6 months
Stock-based compensation expense	$ 1,100,000	$ 948,000	$ 682,000