Risk Management and Use of Derivative Financial Instruments - Derivative Gain Loss Recognized in Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Amount of Gain (Loss) Recognized in Income on Derivatives
Amount of gain (loss) recognized income on derivatives	$ 103	$ (29)	$ 333	$ (178)
Derivatives Not Designated as Hedging Instruments | Stock warrants | Other gains and (losses)
Amount of Gain (Loss) Recognized in Income on Derivatives
Amount of gain (loss) recognized income on derivatives	(33)	33	99	(165)
Derivatives Not Designated as Hedging Instruments | Foreign currency forward contracts | Other gains and (losses)
Amount of Gain (Loss) Recognized in Income on Derivatives
Amount of gain (loss) recognized income on derivatives	194	(25)	260	8
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Interest expense
Amount of Gain (Loss) Recognized in Income on Derivatives
Amount of gain (loss) recognized income on derivatives	(23)	8	(31)	26
Derivatives Not Designated as Hedging Instruments | Swaption | Other gains and (losses)
Amount of Gain (Loss) Recognized in Income on Derivatives
Amount of gain (loss) recognized income on derivatives	0	(86)	0	(134)
Derivatives in Cash Flow Hedging Relationships (a) | Interest rate swaps | Interest expense
Amount of Gain (Loss) Recognized in Income on Derivatives
Amount of gain (loss) recognized income on derivatives	(30)	46	15	92
Derivatives in Cash Flow Hedging Relationships (a) | Foreign currency collars | Other gains and (losses)
Amount of Gain (Loss) Recognized in Income on Derivatives
Amount of gain (loss) recognized income on derivatives	$ (5)	$ (5)	$ (10)	$ (5)