Real Estate Fund Investments - Schedule of Income from Fund Investment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Investment Holdings [Line Items]
Net realized loss	$ (839)		$ (665)
Net unrealized gain (loss)	202	$ (361)	(26)	$ (2,939)
Unconsolidated Real Estate Funds [Member] | Property Fund II [Member]
Investment Holdings [Line Items]
Investment income	2	1,389	3	1,391
Investment expenses	13	668	291	2,051
Net investment (loss) income	(11)	721	(288)	(660)
Net realized loss	(5,020)		(20,221)
Net unrealized gain (loss)	5,031	(40)	51	(31,918)
Income (loss) from real estate fund investments		681	(20,458)	(32,578)
Unconsolidated Real Estate Funds [Member] | Property Fund III [Member]
Investment Holdings [Line Items]
Investment income	303	480	1,444	480
Investment expenses	54	55	171	193
Net investment (loss) income	249	425	1,273	287
Net realized loss	(1,735)		(6,988)
Net unrealized gain (loss)	1,607	177	(1,411)	(10,551)
Income (loss) from real estate fund investments	121	602	(7,126)	(10,264)
Unconsolidated Real Estate Funds [Member] | Property Fund VII [Member]
Investment Holdings [Line Items]
Investment income	479	1,233	1,441	1,233
Investment expenses	120	501	1,156	1,512
Net investment (loss) income	359	732	285	(279)
Net realized loss	(3,809)		(3,875)
Net unrealized gain (loss)	(4,871)	(4,815)	(9,192)	7,929
Income (loss) from real estate fund investments	$ (8,321)	$ (4,083)	$ (12,782)	$ 7,650