Stock Based Compensation Fair Value Assumptions for Stock Options (Details) - Five Year Service Stock Options [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Risk-free interest rate	2.72%	1.96%	1.34%
Expected volatility	32.01%	39.49%	47.20%
Expected term (in years)	5 years 8 months 26 days	5 years 10 months 20 days	5 years 8 months 19 days
Weighted average grant date fair value of options granted during the period	$ 11.31	$ 9.45	$ 7.57