Fair Value Measurements - Nonrecurring Measurements (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Impairment Charges From Continuing Operations      
Impairment charges $ 29,706 $ 1,023 $ 570
Nonrecurring | Level 3      
Impairment Charges From Continuing Operations      
Impairment charges 31,625 1,023 1,336
Nonrecurring | Level 3 | Operating Expenses      
Impairment Charges From Continuing Operations      
Impairment charges 29,706 1,023 570
Real estate | Nonrecurring | Level 3 | Operating Expenses      
Impairment Charges From Continuing Operations      
Fair Value Measurements 14,850 0 0
Impairment charges 29,183 0 0
CMBS | Nonrecurring | Level 3 | Operating Expenses      
Impairment Charges From Continuing Operations      
Fair Value Measurements 400 1,478 1,808
Impairment charges 523 1,023 570
Equity investments in real estate | Nonrecurring | Level 3      
Impairment Charges From Continuing Operations      
Fair Value Measurements 12,528 0 7,662
Impairment charges $ 1,919 $ 0 $ 766