Variable Interest Entities ("VIEs") - Summary of Assets and Liabilities of Variable Interest Entities (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Cash and restricted cash	$ 45,737	$ 55,728
Accounts and other receivables	10,781	7,692
Other assets	9,529	13,121
Total assets	8,954,892	9,030,441
Other liabilities	45,922	43,950
Total liabilities	3,457,071	3,475,488
Variable Interest Entity [Member]
Variable Interest Entity [Line Items]
Investments, at fair value	18,318	17,136
Investments, at cost	63,570	63,550
Cash and restricted cash	4,959	4,976
Accounts and other receivables	501
Other assets	1
Total assets	87,349	85,662
Loans payable to noncontrolling interests	43,981	42,195
Other liabilities	202	131
Total liabilities	$ 44,183	$ 42,326