Securities Purchased under Resale Agreements and Sold under Repurchase Agreements (Balance Sheet Offsetting) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets, Resale Agreements
Gross Amounts of Recognized Assets	$ 1,260,000	$ 1,110,000
Gross Amounts Offset on the Consolidated Balance Sheet	0	(250,000)
Net Amounts of Assets Presented on the Consolidated Balance Sheet	1,260,000	860,000
Securities Purchased under Agreements to Resell Gross Amounts Not Offset [Abstract]
Collateral Received	(1,258,866)	(856,058)
Net Amount	1,134	3,942
Liabilities, Repurchase Agreements
Gross Amounts of Recognized Liabilities	300,000	450,000
Gross Amounts Offset on the Consolidated Balance Sheet	0	(250,000)
Net Amounts of Liabilities Presented on the Consolidated Balance Sheet	300,000	200,000
Securities Sold under Agreements to Repurchase Gross Amounts Not Offset [Abstract]
Collateral Pledged	(300,000)	(200,000)
Net Amount	$ 0	$ 0