Derivatives and Hedging Activities (Derivative Positions for Interest Rate Swaps which Qualify as Hedges) (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Change in Fair Value on Loans Held for Sale	$ (75,000)	$ 413,000	$ (1,534,000)	$ 1,252,000
Fair Value Hedges, Net	0		0		$ 0
Interest Receivable	29,100,000	$ 36,700,000	29,100,000	$ 36,700,000
Derivative, Net Liability Position, Aggregate Fair Value	35,900,000		35,900,000		79,800,000
Exposure to Institutional Counterparties	37,100,000		37,100,000		48,800,000
Exposure To Counterparties Relating To Customer Related Positions	71,800,000		71,800,000		127,200,000
Interest rate collars on loans [Member]
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Derivative, Notional Amount	$ 400,000,000		$ 400,000,000		$ 400,000,000
Derivative, Average Remaining Maturity			1 year 10 months 28 days		2 years 7 months 28 days
Derivative, Average Variable Interest Rate	0.08%		0.08%		0.15%
Fair Value	$ 13,971,000		$ 13,971,000		$ 21,764,000
Derivative, Average Cap Interest Rate	2.73%		2.73%		2.73%
Derivative, Average Floor Interest Rate	2.20%		2.20%		2.20%
Interest rate swaps on loans [Member]
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Derivative, Notional Amount	$ 550,000,000		$ 550,000,000		$ 450,000,000
Derivative, Average Remaining Maturity			2 years 9 months 29 days		2 years 7 months 28 days
Derivative, Average Variable Interest Rate	0.08%		0.08%		0.15%
Derivative, Average Fixed Interest Rate	2.16%		2.16%		2.37%
Fair Value	$ 18,016,000		$ 18,016,000		$ 27,021,000
Interest rate swaps on borrowings [Member]
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Derivative, Notional Amount	$ 75,000,000		$ 75,000,000		$ 75,000,000
Derivative, Average Remaining Maturity			5 months 4 days		1 year 2 months 4 days
Derivative, Average Variable Interest Rate	0.12%		0.12%		0.22%
Derivative, Average Fixed Interest Rate	1.53%		1.53%		1.53%
Fair Value	$ (593,000)		$ (593,000)		$ (1,341,000)
Interest rate swaps
Details of derivative positions for interest rate swaps which qualify as hedges for accounting purposes
Derivative, Notional Amount	1,025,000,000		1,025,000,000		925,000,000
Fair Value	31,394,000		31,394,000		47,444,000
Interest Receivable	1,200,000		1,200,000		1,200,000
Interest Payable, Current	$ (60,000)		$ (60,000)		$ (81,000)