Fair Value of Financial Instruments (Level 3 Liabilities) (Details) - Level 3 - Recurring basis - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Agreements with Non-mark-to-market Collateral Provisions
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 795,341	$ 0	$ 1,159,213	$ 0
Issuances	0	2,036,597	0	2,036,597
Payment of principal	(104,549)	(312,638)	(467,695)	(312,638)
Changes in unrealized losses	(209)	3,448	(935)	3,448
Balance at end of period	690,583	1,727,407	690,583	1,727,407
Agreements with Mark-to-market Collateral Provisions
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	858,066	0	1,124,162	0
Issuances	597,761	1,386,592	989,407	1,386,592
Payment of principal	(180,655)	(156,032)	(838,397)	(156,032)
Changes in unrealized losses	0	1,174	0	1,174
Balance at end of period	$ 1,275,172	$ 1,231,734	$ 1,275,172	$ 1,231,734