Assets Purchased under Resale Agreements and Sold under Repurchase Agreements (Balance Sheet Offsetting) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets, Resale Agreements
Gross Amounts of Recognized Assets	$ 2,299,184	$ 1,460,000
Gross Amounts Offset on the Consolidated Balance Sheet	0	0
Assets Purchased under Agreements to Resell Gross Amounts Not Offset [Abstract]
Collateral Received	(2,285,058)	(1,458,700)
Net Amount	14,126	1,300
Liabilities, Repurchase Agreements
Gross Amounts of Recognized Liabilities	300,000	300,000
Gross Amounts Offset on the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented on the Consolidated Balance Sheet	300,000	300,000
Assets Sold under Agreements to Repurchase Gross Amounts Not Offset [Abstract]
Collateral Pledged	(300,000)	(300,000)
Net Amount	0	0
Assets purchased under resale agreements (“resale agreements”)	$ 2,299,184	$ 1,460,000