Variable Interest Entities and Noncontrolling Interests - Income or loss attributable to third party investors (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Noncontrolling Interest [Abstract]
Amounts attributable to non-redeemable noncontrolling interests	$ (8,116)	$ (9,346)	$ (19,492)	$ (25,670)
Dividends attributable to redeemable noncontrolling interests	(4,585)	(4,586)	(9,170)	(9,170)
Net (income) loss attributable to noncontrolling interests	$ (12,701)	$ (13,932)	$ (28,662)	$ (34,840)