Investment Securities (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Schedule of Investments [Line Items]
Other than Temporary Impairment Losses, Investments			$ 0	$ 0
Debt Securities, Available-for-sale, Amortized Cost	$ 1,519,098,000		1,519,098,000		$ 1,007,834,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	0		$ 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		$ 140,900,000	$ 0	196,400,000
Debt Securities, Realized Gain (Loss)	0	(27,000)	0	3,286,000
Debt Securities, Available for Sale, Sold at Loss, Amortized Cost Amount		112,500,000		112,500,000
Debt Securities, Available-for-sale, Realized Gain		37,000		3,400,000
Debt Securities, Available-for-sale, Realized Loss		$ 64,000		$ 64,000
U.S. Government Sponsored Entities Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	844,128,000		844,128,000		726,589,000
Collateral Pledged [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Restricted	$ 717,500,000		$ 717,500,000		$ 691,000,000