Operating Segments - Profit by Reportable Segment to Net Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Profit from reportable segments	$ 4,020	$ (1,537)	$ 635	$ (3,146)	$ (8,048)	$ 449	$ (2,692)	$ 2,639	$ (28)	$ (7,652)	$ 44,271
Depreciation and amortization									(18,579)	(15,585)	(30,749)
General and administrative									(9,287)	(8,704)	(11,359)
(Loss) gain on foreign currency transactions									(13,378)	(15,108)	12,399
Loss on extinguishment of debt									0	(5,219)	0
Equity in (loss) income from unconsolidated joint ventures									(519)	(2,758)	1,129
Gain on sale or write-down of assets, net									32,107	14,809	171,530
Income tax provision									(4)	2,000	(3,210)
Net income (loss)									7,464	(26,137)	183,040
Operating segments
Segment Reporting Information [Line Items]
Profit from reportable segments									27,549	21,018	54,524
Other non-segment items of income (expense)
Segment Reporting Information [Line Items]
Depreciation and amortization									(14,755)	(13,379)	(22,761)
General and administrative									(9,287)	(8,704)	(11,359)
Advisory fee to related party									(8,648)	(8,410)	(11,294)
Other income									5,113	1,823	35,161
Interest income									18,660	19,607	15,793
Interest expense									(29,374)	(31,816)	(58,872)
(Loss) gain on foreign currency transactions									(13,378)	(15,108)	12,399
Loss on extinguishment of debt									0	(5,219)	0
Equity in (loss) income from unconsolidated joint ventures									(519)	(2,758)	1,129
Gain on sale or write-down of assets, net									32,107	14,809	171,530
Income tax provision									(4)	2,000	(3,210)
Net income (loss)									$ 7,464	$ (26,137)	$ 183,040