Fair Value Measurements and Derivative Instrument (Significant Assumptions and Inputs on Stock Appreciation Right Liability) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility (as a percent)		37.50%
Risk-free interest rate		2.10%
Stock Appreciation Rights (SARs)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Stock Price (USD per share)	$ 39.02	$ 19.45
Stock Appreciation Rights (SARs) | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contractual term (in years)	1 year 1 month	2 years 1 month
Volatility (as a percent)	25.00%
Risk-free interest rate	1.30%
Stock Appreciation Rights (SARs) | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contractual term (in years)	5 years 1 month	6 years 1 month
Volatility (as a percent)	37.50%
Risk-free interest rate	2.20%