Fair Value of Assets and Liabilities - Not Measured at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 5,017,420	$ 4,863,542
Total liabilities	4,716,276	4,575,556
Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Total liabilities	0	0
Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	284,300	297,211
Total liabilities	0	0
Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	4,733,120	4,566,331
Total liabilities	4,716,276	4,575,556
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	583,842	623,531
Restricted cash	104,485	80,733
Deposits	872	871
Total assets	689,199	705,135
Accrued expenses and other liabilities	1,699
Accounts payable	5,860	5,542
Payables to investors	71,917	73,162
Total liabilities	79,476	78,704
Portion at Other than Fair Value Measurement | Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Restricted cash	0	0
Deposits	0	0
Total assets	0	0
Accrued expenses and other liabilities	0
Accounts payable	0	0
Payables to investors	0	0
Total liabilities	0	0
Portion at Other than Fair Value Measurement | Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	583,842	623,531
Restricted cash	104,485	80,733
Deposits	872	871
Total assets	689,199	705,135
Accrued expenses and other liabilities	0
Accounts payable	5,860	5,542
Payables to investors	71,917	73,162
Total liabilities	77,777	78,704
Portion at Other than Fair Value Measurement | Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Restricted cash	0	0
Deposits	0	0
Total assets	0	0
Accrued expenses and other liabilities	1,699
Accounts payable	0	0
Payables to investors	0	0
Total liabilities	1,699	0
Balance at Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	583,842	623,531
Restricted cash	104,485	80,733
Deposits	872	871
Total assets	689,199	705,135
Accrued expenses and other liabilities	1,699
Accounts payable	5,860	5,542
Payables to investors	71,917	73,162
Total liabilities	$ 79,476	$ 78,704