Stock Option Black Scholes Option Pricing Model Assumptions (Details) - Employee Stock Option [Member] - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Expected volatility	29.00%	33.70%	32.50%	33.50%
Risk-free interest rate	1.80%	1.30%	2.00%	1.30%
Expected term (years)	5 years 6 months	5 years 6 months 1 day	5 years 5 months 15 days	5 years 5 months 15 days
Granted, Weighted Average Grant Date Fair Value	$ 21.84	$ 17.37	$ 21.98	$ 13.27