Commitments, Off-Balance Sheet Arrangements, Legal Proceedings and Regulatory Matters (Details Textuals) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jan. 01, 2020	Dec. 31, 2018
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Allowance for Unfunded Commitments	$ 57,276,000		$ 57,276,000		$ 21,907,000
Expense Related to Qualified Affordable Housing Projects	6,000,000	$ 4,000,000	18,000,000	$ 14,000,000
Remaining Investment in Qualified Affordable Housing Projects	274,000,000		274,000,000		234,000,000
Variable Interest Entity Reporting Entity Involvement Unfunded Obligation Amount	147,000,000		147,000,000		123,000,000
Qualified Affordable Housing Investments, Impairment Loss			0		0
Loans Repurchased Under Make Whole Requests	7,000,000		$ 7,000,000		$ 2,000,000
Loans Sold To Outside Investors Loss ReimbursementSettlement Paid			no		negligible
Loans Sold To Outside Investors Original Amount	14,000,000,000.0		$ 14,000,000,000.0
Loans Sold To Outside Investors Remaining Outstanding Amount	7,200,000,000		7,200,000,000
Unfunded Commitments	57,276,000		57,276,000		$ 21,907,000
Mortgage Repurchase Reserve	2,000,000		2,000,000		795,000
Residential Mortgage Loans Sold With Recourse Risk	47,000,000		47,000,000		39,000,000
Residential Mortgage Loans Sold With Credit Recourse Risk	36,000,000		36,000,000		45,000,000
SEC Schedule, 12-09, Reserve, Off-balance Sheet Activity [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Provision for unfunded commitments			17,000,000		(2,500,000)
Unfunded Commitments					21,907,000		$ 24,336,000
UnconsolidatedProjectsLowIncomeHousing [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Other Investments	285,000,000		285,000,000		248,000,000
PrincipalInvestmentCommitment [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Other Investments	$ 28,000,000		$ 28,000,000		$ 26,000,000
Accounting Standards Update 2016-13 | Cumulative Effect, Period Of Adoption, Adjustment
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Allowance for Unfunded Commitments						$ 18,690,000