Stock Based Compensation (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Notes to Financial Statements [Abstract]
Percentage of eligible earnings to purchase common stock through the employee stock purchase plan	10.00%
Discount on the average closing price for the employee stock purchase plan	5.00%
Stock Based Compensation Expense Table
Stock based compensation	$ 12,977,000	$ 9,954,000
Tax effect recognized in net income	4,542,000	3,484,000
Windfall tax benefit/(shortfall), net	4,312,000	7,415,000
Employee stock options granted during the period	447,850	383,600
Weighted average assumptions used to value option grants Table
Fair value per share ($)	$ 36.53	$ 29.65
Risk-free interest rate (%)	0.80%	0.82%
Expected option life (years)	5 years 2 months 5 days	5 years 2 months 19 days
Expected volatility (%)	36.29%	36.56%
Expected dividend yield (%)	0.57%	0.59%
Cash received from exercise of options	9,100,000	16,900,000
Restricted stock awards granted during period	261,390	258,057
Weighted average fair value per share of restricted stock awards granted during the period	$ 115.36	$ 93.62
Restricted stock awards vested during period	103,795
Weighted average grant date fair value per share	$ 57.64
Weighted average vest date fair value per share	$ 120.14
Shares of stock purchased during the period by participants in the employee stock purchase plan	5,594	6,764
Amount paid for stock purchased during the period by participants in the employee stock purchase plan	$ 640,000	$ 600,000