Transactions with Affiliates - Other Transactions, Reimbursement of Common Overhead Expenses (Details) - PMT - USD ($)		12 Months Ended
	Sep. 12, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 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		$ 10,182,000	$ 6,233,000	$ 7,563,000
Payments and settlements during the period		177,116,000	71,943,000	64,945,000
Common overhead incurred
Reimbursement of common overhead and expenses incurred on behalf of affiliates
Reimbursement of common overhead and expenses incurred by the Company		5,340,000	4,640,000	5,306,000
Compensation
Reimbursement of common overhead and expenses incurred on behalf of affiliates
Reimbursement of common overhead and expenses incurred by the Company		480,000	480,000
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		$ 4,362,000	$ 1,113,000	$ 2,257,000