Other Assets and Liabilities - Summary of Components of Other Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Other Liabilities [Abstract]
Accrued dividends payable	$ 67,080	$ 66,888
Accrued management and incentive fees payable	15,492	14,284
Accrued interest payable	22,104	14,162
Derivative liabilities	2,166	4,911
Accounts payable and other liabilities	2,782	2,125
Secured debt repayments pending servicer remittance		38,456
Total	$ 109,624	$ 140,826