Stock Based Compensation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Notes to Financial Statements [Abstract]
Percentage of eligible earnings to purchase common stock through the employee stock purchase plan	1000.00%		1000.00%
Discount on the average closing price for the employee stock purchase plan			500.00%
Stock Based Compensation Expense Table
Stock based compensation	$ 7,660	$ 6,280	$ 23,466	$ 19,384
Tax effect recognized in net income	2,681	2,198	8,216	6,789
Windfall tax benefit/(shortfall), net	372	1,369	3,999	4,241
Employee stock options granted during the period			753,500	595,850
Weighted average assumptions used to value option grants Table
Fair value per share ($)			$ 24.45	$ 16.93
Risk-free interest rate (%)			191.00%	234.00%
Expected option life (years)			5.34	5.38
Expected volatility (%)			3526.00%	3454.00%
Expected dividend yield (%)			60.00%	72.00%
Cash received from exercise of options			14,479	16,955
Restricted stock awards granted during period			339,330	252,893
Weighted average fair value per share of restricted stock awards granted during the period			$ 74.27	$ 52.65
Restricted stock awards vested during period			213,101
Weighted average grant date fair value per share			$ 51.79
Weighted average vest date fair value per share			$ 76.50
Shares of stock purchased during the period by participants in the employee stock purchase plan			20,628	22,598
Amount paid for stock purchased during the period by participants in the employee stock purchase plan			$ 1,600	$ 1,200