Other Expenses - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Management fee - percent of outstanding equity balance			1.50%
Incentive fee computation-percent of the product per agreement			20.00%
Incentive fee computation-percent of outstanding Equity per annum			7.00%
Management fees description			Manager is entitled to an incentive fee in an amount equal to the product of (i) 20% and (ii) the excess of (a) our Core Earnings (as defined in our Management Agreement) for the previous 12 month period over (b) an amount equal to 7.00% per annum multiplied by our outstanding Equity, provided that our Core Earnings over the prior three-year period is greater than zero. Core Earnings, as defined in our Management Agreement, is generally equal to our net income (loss) prepared in accordance with GAAP, excluding (i) certain non-cash items (ii) the net income (loss) related to our legacy portfolio and (iii) incentive management fees.
Management fees	$ 22,388	$ 14,393	$ 37,880	$ 27,314
Accrued management and incentive fees payable	22,388		22,388		$ 14,284
Manager [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Management fees	11,100	9,600	22,200	19,100
Total incentive compensation payments	11,300	$ 4,800	15,700	$ 8,200
Accrued management and incentive fees payable	$ 22,400		$ 22,400		$ 14,300