Loans, Allowance for Credit Losses and Credit Quality Textual (Details) - USD ($)	3 Months Ended				9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Days To Be Termed As Non Accrual Loans					90 days
Financing Receivable, Allowance for Credit Loss, Period Increase (Decrease) by percentage	3.10%				70.60%
Provision for credit losses	$ 7,500,000	$ 20,000,000.0	$ 25,000,000.0	$ 0	$ 52,500,000	$ 2,000,000
Loans with active Deferrals	583,800,000				583,800,000
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method					(1,137,000)
Financing Receivable, Allowance for Credit Loss, Purchased with Credit Deterioration, Increase					1,157,000
Interest Receivable	36,700,000				36,700,000
Loans and Leases Receivable, Allowance	(115,625,000)			(66,942,000)	(115,625,000)	(66,942,000)	$ (67,740,000)	$ (65,960,000)	$ (64,293,000)
Off-Balance Sheet, Credit Loss, Liability	1,000,000.0				1,000,000.0
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	(3,400,000)				(47,900,000)
Financing Receivable, Troubled Debt Restructuring, Subsequent Default	0			0	0	0
US Government Insured Loan Program [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, before Allowance for Credit Loss	811,700,000				811,700,000
Commercial And Industrial [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Provision for credit losses				$ (528,000)		$ 445,000
Financing Receivable, before Allowance for Credit Loss	2,062,345,000				2,062,345,000		$ 1,395,036,000
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method					(1,984,000)
Financing Receivable, Allowance for Credit Loss, Purchased with Credit Deterioration, Increase					49,000
Loans and Leases Receivable, Allowance	$ (17,332,000)				$ (17,332,000)			$ (16,857,000)	$ (15,760,000)