Stock Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock Based Compensation Expense [Abstract]
Stock based compensation	$ 22,815	$ 20,113	$ 43,864	$ 39,092
Tax effect recognized in net income	$ 7,985	$ 7,040	$ 15,352	$ 13,682
Stock Options [Member]
Stock Based Compensation Expense [Abstract]
Employee stock options granted during the period (in shares)			520,600	584,500
Fair value per share (in dollars per share)			$ 40.42	$ 34.44
Weighted average assumptions used to value option grants [Abstract]
Risk-free interest rate			2.05%	1.39%
Expected option life			5 years 3 months 6 days	5 years 2 months 12 days
Expected volatility			18.81%	21.63%
Expected dividend yield			0.68%	0.70%
Cash received from exercise of options			$ 26,900	$ 10,000
Restricted Stock Awards [Member]
Weighted average assumptions used to value option grants [Abstract]
Restricted stock awards granted during period (in shares)			316,667	378,180
Weighted average fair value per share of restricted stock awards granted during the period (in dollars per share)			$ 196.28	$ 168.68
Restricted stock awards vested during period (in shares)			124,600
Weighted average grant date fair value per share (in dollars per share)			$ 143.89
Weighted average vest date fair value per share (in dollars per share)			$ 213.08
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of eligible earnings to purchase common stock through the employee stock purchase plan	10.00%		10.00%
Discount on the average closing price for the employee stock purchase plan			5.00%
Weighted average assumptions used to value option grants [Abstract]
Shares of stock purchased during the period by participants in the employee stock purchase plan (in shares)			10,426	9,964
Amount paid for stock purchased during the period by participants in the employee stock purchase plan			$ 2,040	$ 1,720