Derivative Financial Instruments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 31, 2017	Oct. 31, 2015
Debt Instrument [Line Items]
Gain upon settlement of cash flow hedges (less than $0.1 million)	$ 100,000	$ 100,000	$ 100,000
2015 Interest Rate Swap
Debt Instrument [Line Items]
Notional amount					$ 262,500,000
Derivative fixed interest rate					1.46%
2015 Credit Facility
Debt Instrument [Line Items]
Amount of hedged item					$ 262,500,000
Credit facility borrowing capacity				$ 350,000,000
Derivatives Designated as Hedging Instruments: | Recurring
Debt Instrument [Line Items]
Net derivative asset	$ 3,300,000