Consolidation - Revenue and Expenses of Consolidated Investment Product (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income:
Total revenues	$ 128,024	$ 123,675	$ 94,132	$ 79,776	$ 79,850	$ 82,324	$ 80,085	$ 80,295	$ 425,607	$ 322,554	$ 381,977
Expenses:
Net Income (Loss) Attributable to Common Stockholders	$ 3,414	$ 16,708	$ (2,389)	$ 10,943	$ 12,426	$ 15,625	$ 8,088	$ 12,363	28,676	$ 48,502	$ 35,106
CLOs
Income:
Realized and unrealized gain (loss), net									7,270
Interest Income									45,526
Other income									1,552
Total revenues									54,348
Expenses:
Other operating expenses									6,684
Interest expense									35,243
Total Expense									41,927
Noncontrolling interest									(1,507)
Net Income (Loss) Attributable to Common Stockholders									$ 10,914