Other Expenses - Schedule of General and Administrative Expenses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Professional services	$ 3,812	$ 3,311	$ 3,156
Operating and other costs	1,903	2,147	2,709
Subtotal	5,715	5,458	15,488
Non-cash and CT Legacy Portfolio compensation expenses
Restricted class A common stock earned	23,593	19,052	12,966
Subtotal	24,031	22,089	20,888
Other expenses	176	169	333
General and administrative expenses	29,922	27,716	36,709
General Electrical Capital Corporation [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
GE transaction costs			9,623
General and Administrative Expense [Member]
Non-cash and CT Legacy Portfolio compensation expenses
Director stock-based compensation	438	375	375
Manager [Member]
Non-cash and CT Legacy Portfolio compensation expenses
Management incentive awards plan	16,200	18,000	10,700
General and administrative expenses	$ 29,746	27,547	36,376
CT Legacy Partners [Member]
Non-cash and CT Legacy Portfolio compensation expenses
Management incentive awards plan		1,094	2,177
CT Opportunity Partners I, LP [Member]
Non-cash and CT Legacy Portfolio compensation expenses
Management incentive awards plan		$ 1,568	$ 5,370