Equity Compensation Plans - Weighted-Average Assumptions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input of stock options (as a percent)	0.027	0.022	0.018
Expected life
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Term of stock options	5 years 5 months 28 days	5 years 5 months 19 days	5 years 5 months 19 days
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input of stock options (as a percent)	0.34	0.33	0.42
Expected dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input of stock options (as a percent)	0.00	0.00	0.00