Derivative Financial Instruments Derivative Financial Instruments Narrative (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jun. 30, 2012 USD ($)
Derivative [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (170,478,000)	$ (229,327,000)
Long-term Debt	319,477,000
Secured Debt [Member]
Derivative [Line Items]
Long-term Debt	619,477,000	305,292,000
Accumulated Other Comprehensive Income, Net Unrealized Gain (Loss) on Nonderivative Instruments [Member]
Derivative [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (14,380,000)	$ (14,380,000)	$ (14,380,000)	$ (14,380,000)
Number of Counterparties [Member]
Derivative [Line Items]
Description of Derivative Activity Volume	three	three
London Interbank Offered Rate (LIBOR) [Member] | Secured Debt [Member]
Derivative [Line Items]
Long-term Debt	$ 254,100,000
Interest Rate Swap [Member]
Derivative [Line Items]
Number of Interest Rate Derivatives Held	1				6
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 700,000
Derivative, Notional Amount			$ 214,000,000		$ 200,000,000
Derivative, Fixed Interest Rate			1.42%		1.00%
Interest Rate Cap [Member]
Derivative [Line Items]
Number of Interest Rate Derivatives Held	3
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 300,000
Derivative, Cap Interest Rate	2.00%		2.00%
Derivative, Notional Amount	$ 100,000,000		$ 100,000,000
Derivative Purchase Price			$ 1,700,000
Interest Rate Cap [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held		2
Forward Contracts [Member]
Derivative [Line Items]
Description of Derivative Activity Volume	54
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Minimum [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 158,000
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Maximum [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 39,500,000