Stock-Based Compensation - Assumptions Used in Options Pricing Model (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of assumptions used in option models
Risk-free interest rate, minimum	2.07%	0.91%	0.56%
Risk-free interest rate, maximum	3.06%	2.61%	1.86%
Weighted-average volatility	22.00%	22.00%	24.00%
Dividend yield	2.10%	2.22%	2.12%
Minimum
Summary of assumptions used in option models
Expected years until exercise	7 years 6 months	7 years 2 months 12 days	6 years 10 months 25 days
Maximum
Summary of assumptions used in option models
Expected years until exercise	8 years 4 months 24 days	7 years 10 months 24 days	7 years 8 months 12 days