Fair Value of Financial Instruments (Level 3 Liabilities) (Details) - Level 3 - Recurring basis - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 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	$ 0
Transfer from Level 2	2,036,597
Issuances	0
Payment of principal	(879,698)
Changes in unrealized losses	2,314
Balance at end of period	0	$ 1,159,213
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	0
Transfer from Level 2	1,386,592
Issuances	258,322
Payment of principal	(520,752)
Changes in unrealized losses	0
Balance at end of period	$ 0	$ 1,124,162