Derivative Instruments - Realized and Unrealized Gain (Loss) on Derivatives Not Designated as Hedging Instruments (Details) - Derivatives not designated as hedging instruments: - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Unrealized Gain (Loss)	$ 69	$ (19,765)	$ (37,611)	$ 19,621
Realized (Loss) Gain	(213)	(165)	129,723	(434)
Total (Loss) Gain	(144)	(19,930)	92,112	19,187
Contingent redemption features - Series A Preferred Stock
Derivative [Line Items]
Unrealized Gain (Loss)	0	(19,974)	(42,140)	19,468
Realized (Loss) Gain	0	0	140,320	0
Total (Loss) Gain	0	(19,974)	98,180	19,468
Cross currency and interest rate swaps
Derivative [Line Items]
Unrealized Gain (Loss)	33	151	4,391	24
Realized (Loss) Gain	(213)	(165)	(10,597)	(434)
Total (Loss) Gain	(180)	(14)	(6,206)	(410)
Interest rate swaps
Derivative [Line Items]
Unrealized Gain (Loss)	36	58	138	129
Total (Loss) Gain	$ 36	$ 58	$ 138	$ 129