Variable Interest Entities ("VIEs") - Summary of Assets and Liabilities of Variable Interest Entities (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Cash and restricted cash	$ 92,696	$ 55,728
Accounts and other receivables	12,313	7,692
Total assets	8,986,806	9,030,441
Other liabilities	44,958	43,950
Total liabilities	3,451,940	3,475,488
Variable Interest Entity [Member]
Variable Interest Entity [Line Items]
Investments, at fair value	16,854	17,136
Investments, at cost	63,587	63,550
Cash and restricted cash	871	4,976
Accounts and other receivables	454
Total assets	81,766	85,662
Loans payable to noncontrolling interests	44,822	42,195
Other liabilities	309	131
Total liabilities	$ 45,131	$ 42,326