Derivative Financial Instruments Narrative (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) contracts	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($) contracts
Net unrealized loss on hedging instruments	$ 193,209		$ 229,327
Secured Debt [Member]
Total debt	324,997		305,292
Accumulated Other Comprehensive Income, Net Unrealized Gain (Loss) on Nonderivative Instruments [Member]
Net unrealized loss on hedging instruments	$ 14,380	$ 14,380	$ 14,380	$ 14,380
Number of Counterparties [Member]
Derivative Counterparties	3		3
London Interbank Offered Rate (LIBOR) [Member] | Secured Debt [Member]
Total debt	$ 262,500
Interest Rate Swap [Member]
Number of Interest Rate Derivatives Held | contracts	1			6
Derivative, Notional Amount	$ 214,000			$ 200,000
Pay fixed interest rate in interest rate swap	1.42%			1.00%
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ (100)
Interest Rate Cap [Member]
Number of Interest Rate Derivatives Held | contracts	3
Derivative, Notional Amount	$ 100,000
Derivative, Cap Interest Rate	2.00%
Derivative Purchase Price		$ 1,700
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ (300)
Forward Contracts [Member]
Description of Derivative Activity Volume	53
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Minimum [Member]
Derivative, Notional Amount	$ 118
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Maximum [Member]
Derivative, Notional Amount	$ 45,500