Stock-Based Compensation - Stock Option Black Scholes Option Pricing Model Assumptions (Details) - Employee Stock Option [Member]	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Expected volatility	30.50%	32.50%	33.50%
Risk-free interest rate	2.80%	2.00%	1.30%
Expected term (years)	6 years 1 month 6 days	5 years 6 months	5 years 6 months