Other Assets and Liabilities - Summary of Components of Other Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other Liabilities [Abstract]
Accrued dividends payable	$ 66,888	$ 58,615
Secured debt repayments pending servicer remittance	38,456	5,372
Accrued management and incentive fees payable	14,284	12,798
Accrued interest payable	14,162	9,049
Derivative liabilities	4,911	210
Accounts payable and other liabilities	2,125	1,775
Total	$ 140,826	$ 87,819