Share Based Award Stock Options Granted and Valuation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Time-based stock option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options granted	8,825	13,405	22,816
Time based options grant date fair value	$ 375	$ 413	$ 590
Expected term (years)	5 years 6 months	5 years 6 months	5 years 7 months
Expected stock price volatility	27.00%	31.80%	25.90%
Risk-Free Interest Rate	1.10%	0.70%	1.70%
Expected Dividend Yield	0.00%	0.00%	0.00%
Weighted Average Exercise Price	$ 158.20	$ 101.32	$ 93.30
Weighted Average Grant Date Fair Value per option	$ 42.51	$ 30.78	$ 25.86
Performance stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options granted			244,825
Performance Shares Earned		244,825	349,812
Performance stock options total grant date fair value			$ 6,087
Expected term (years)			3 years
Expected stock price volatility			30.86%
Risk-Free Interest Rate			2.30%
Expected Dividend Yield			0.00%
Weighted Average Exercise Price			$ 91.88
Weighted Average Grant Date Fair Value per option			$ 24.86