Investment Securities (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Schedule of Investments [Line Items]
Other than Temporary Impairment Losses, Investments			$ 0	$ 0
Asset backed securities mortgage portfolio, term			15 years
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%
Debt Securities, Available-for-sale, Amortized Cost	$ 980,047,000		$ 980,047,000		$ 1,187,499,000
Debt Securities, Available-for-sale, Realized Gain (Loss)	(27,000)	$ 186,000	3,286,000	(421,000)
Debt Securities, Available-for-sale, Realized Gain	37,000	253,000	3,400,000	271,000
Debt Securities, Available-for-sale, Realized Loss	64,000	67,000	64,000	692,000
Debt Securities, Held-to-maturity, Transfer, Amount				373,900,000
Debt Securities, Available for Sale, Sold at Gain, Amortized Cost Amount	140,900,000	23,800,000	196,400,000	29,100,000
Debt Securities, Available for Sale, Sold at Loss, Amortized Cost Amount	112,500,000	$ 10,700,000	112,500,000	$ 62,400,000
U.S. Government Sponsored Entities Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	698,237,000		698,237,000		884,571,000
Collateral Pledged [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Restricted	$ 688,000,000		$ 688,000,000		$ 585,000,000