Transactions with Affiliates - Other Transactions, Reimbursement of Common Overhead Expenses (Details) - PMT - USD ($)		3 Months Ended		9 Months Ended
	Sep. 12, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Transactions with Affiliates
Expense reimbursement amount, per quarter, relating to personnel	$ 120,000
Reimbursement of common overhead and expenses incurred on behalf of affiliates
Reimbursement of common overhead and expenses incurred by the Company		$ 1,857,000	$ 1,389,000	$ 4,333,000	$ 5,069,000
Payments and settlements during the period		21,650,000	22,786,000	45,265,000	63,249,000
Common overhead incurred
Reimbursement of common overhead and expenses incurred on behalf of affiliates
Reimbursement of common overhead and expenses incurred by the Company		1,210,000	1,193,000	3,387,000	4,220,000
Compensation
Reimbursement of common overhead and expenses incurred on behalf of affiliates
Reimbursement of common overhead and expenses incurred by the Company		120,000		360,000
Expenses incurred by related party (reporting entity), net
Reimbursement of common overhead and expenses incurred on behalf of affiliates
Reimbursement of common overhead and expenses incurred by the Company		$ 527,000	$ 196,000	$ 586,000	$ 849,000