Stock Based Compensation Share-based Compensation - Summary of Weighted Average Valuation Assumptions for Market Condition Performance Restricted Stock Units (Details) - Market Condition Based PRSUs	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Expected life (years)	2 years 10 months 10 days	2 years 10 months 10 days	2 years 10 months 6 days
Risk free interest rate	2.38%	1.40%	0.88%
Volatility	21.79%	23.78%	28.00%