Stock-Based Compensation - Weighted-Average Assumptions Used To Determine Fair Value Of SARs Grants On Date Of Grant Using Black-Scholes-Merton Valuation Model (Details) - Stock appreciation rights	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
Expected stock price volatility	21.00%	22.00%	22.00%
Risk-free interest rate	2.50%	1.80%	1.10%
Expected life in years	4 years 6 months 8 days	4 years 6 months 11 days	4 years 4 months 21 days