Other Assets and Liabilities - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Manager [Member]
Schedule Of Other Assets [Line Items]
Accrued management and incentive fees payable	$ 12.8	$ 14.4
Other Liabilities [Member]
Schedule Of Other Assets [Line Items]
Secured debt repayments pending servicer remittance	5.4
Accrued dividends payable	58.6	58.1
Other Liabilities [Member] | Manager [Member]
Schedule Of Other Assets [Line Items]
Accrued management and incentive fees payable	$ 12.8	$ 14.4