Fair Value Measurements - Nonrecurring Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Impairment Charges From Continuing Operations
Impairment charges	$ 6,571		$ 13,600	$ 29,183
Nonrecurring | Level 3 | Equity investments in real estate
Impairment Charges From Continuing Operations
Fair Value Measurements	6,809	$ 0	11,589	0
Impairment charges	6,295	0	8,805	0
Nonrecurring | Level 3 | Real estate
Impairment Charges From Continuing Operations
Fair Value Measurements	0	14,850	4,719	14,850
Impairment charges	0	29,183	4,519	29,183
Nonrecurring | Level 3 | CMBS
Impairment Charges From Continuing Operations
Fair Value Measurements	637	0	637	0
Impairment charges	$ 276	$ 0	$ 276	$ 0