Investment Securities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule of Investments [Line Items]
Other than Temporary Impairment Losses, Investments	$ 0	$ 0
Debt Securities, Available-for-sale, Amortized Cost	1,080,988		$ 1,007,834
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 0
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%
Debt Securities, Available for Sale, Sold at Gain, Amortized Cost Amount	$ 0
U.S. Government Sponsored Entities Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	800,312		726,589
Collateral Pledged [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Restricted	$ 747,000		$ 691,000