Stock-Based Compensation (Details 3) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Employee Stock Purchase Plan
Assumptions used in determining the fair value of the stock-based awards
Risk-free interest rate (as a percent)	0.10%	0.10%	0.10%	0.10%
Expected Volatility, (as a percent)	31.80%	31.00%	31.80%	31.00%
Expected life	6 months	6 months	6 months	6 months
Expected dividends (as a percent)	0.00%	0.00%	0.00%	0.00%
Stock Options / Stock Appreciation Rights
Assumptions used in determining the fair value of the stock-based awards
Risk-free interest rate, minimum (as a percent)	0.50%	0.60%	0.50%	0.60%
Risk-free interest rate, maximum (as a percent)	1.00%	1.00%	1.00%	1.20%
Volatility, minimum (as a percent)	33.40%	38.40%	33.40%	38.40%
Volatility, maximum (as a percent)	38.50%	39.70%	38.80%	42.60%
Expected dividends (as a percent)	0.00%	0.00%	0.00%	0.00%
Number of Shares
Outstanding at beginning of year (in shares)			7,668
Options and SARs granted (in shares)			1,152
Options and SARs exercised (in shares)			(2,050)
Options and SARs canceled (in shares)			(220)
Outstanding at end of period (in shares)	6,550		6,550
Exercisable at end of period (in shares)	3,215		3,215
Weighted Average Exercise Price
Outstanding at beginning of year (in dollars per share)			$ 19.82
Options and SARs granted (in dollars per share)	$ 30.49		$ 30.49
Options and SARs exercised (in dollars per share)	$ 15.71		$ 15.71
Options and SARs canceled (in dollars per share)	$ 25.51		$ 25.51
Outstanding at end of period (in dollars per share)	$ 22.79		$ 22.79
Exercisable at end of period (in dollars per share)	$ 18.74		$ 18.74
Weighted average remaining contractual life of options and SARs outstanding, at end of period			11 days
Weighted average remaining contractual life of options and SARs exercisable, at end of period			11 days
Aggregate intrinsic value of options and SARs outstanding	$ 80,371		$ 80,371
Aggregate intrinsic value of options and SARs exercisable	52,460		52,460
Additional disclosure about options and SARs
Closing price of stock (in dollars per share)	$ 35.06		$ 35.06
Weighted average grant date fair value (in dollars per share)	$ 10.45	$ 9.38	$ 10.45	$ 9.38
Total intrinsic value of awards exercised			26,518	6,578
Stock Options / Stock Appreciation Rights | Maximum
Assumptions used in determining the fair value of the stock-based awards
Expected life	5 years 22 days	5 years 1 month 20 days	5 years 22 days	5 years 1 month 20 days
Stock Options / Stock Appreciation Rights | Minimum
Assumptions used in determining the fair value of the stock-based awards
Expected life	3 years 11 months 8 days	4 years 7 days	3 years 11 months 8 days	4 years 7 days
Options
Additional disclosure about options and SARs
Cash received from exercises			$ 16,212	$ 3,269