Other Assets and Liabilities - Summary of Components of Other Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Other Liabilities [Abstract]
Accrued dividends payable	$ 58,793		$ 58,615
Accrued interest payable	19,922		9,049
Accrued management and incentive fees payable	13,243		12,798
Derivative liabilities	7,167	$ 7,167	210
Accounts payable and other liabilities	2,633		1,775
Secured debt repayments pending servicer remittance			5,372
Total	$ 101,758		$ 87,819