Investments - Summary of Total Impairment Losses Recognized (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Investments in and Advances to Affiliates, Schedule of Investments [Abstract]      
Real estate and intangible asset impairment $ 40,728 $ 6,829 $ 10,923
Loans and Leases Receivable, Impairments, Net (4,820) 487 2,809
Write-off of lease intangibles due to lease terminations 0 (367) (180)
Other impairment 528 0 0
Impairments $ 36,436 $ 6,949 $ 13,552