Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
LOANS AND LEASES
Balance at Beginning of Period	$ 210,200,000	$ 110,800,000	$ 104,500,000	$ 112,600,000
Charge-Offs	(800,000)	(1,100,000)	(3,000,000.0)	(2,700,000)
Recoveries	1,200,000	1,700,000	5,300,000	5,700,000
Net (Charge-Offs) Recoveries	400,000	600,000	2,300,000	3,000,000.0
Provision for Credit Losses	4,800,000	(5,700,000)	110,800,000	(9,900,000)
Balance at End of Period	215,400,000	105,700,000	215,400,000	105,700,000
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	49,000,000.0	23,300,000	19,900,000	25,600,000
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Net (Charge-Offs) Recoveries	0	0	0	0
Provision for Credit Losses	(4,100,000)	(1,300,000)	16,100,000	(3,600,000)
Balance at End of Period	44,900,000	22,000,000.0	44,900,000	22,000,000.0
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	6,500,000		0
Charge-Offs	0		0
Recoveries	0		0
Net (Charge-Offs) Recoveries	0		0
Provision for Credit Losses	400,000		300,000
Balance at End of Period	6,900,000		6,900,000
OTHER FINANCIAL ASSETS
Balance at Beginning of Period	1,300,000		0
Charge-Offs	0		0
Recoveries	0		0
Net (Charge-Offs) Recoveries	0		0
Provision for Credit Losses	(600,000)		300,000
Balance at End of Period	700,000		700,000
TOTAL
Balance at Beginning of Period	267,000,000.0	134,100,000	124,400,000	138,200,000
Charge-Offs	(800,000)	(1,100,000)	(3,000,000.0)	(2,700,000)
Recoveries	1,200,000	1,700,000	5,300,000	5,700,000
Net (Charge-Offs) Recoveries			2,300,000	3,000,000.0
Provision for Credit Losses	500,000	(7,000,000.0)	127,500,000	(13,500,000)
Balance at End of Period	267,900,000	$ 127,700,000	267,900,000	$ 127,700,000
Corporate Debt
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	500,000		0
Provision for Credit Losses	200,000		(100,000)
Balance at End of Period	700,000		700,000
TOTAL
Provision for Credit Losses	$ 0		0
Cumulative Effect Adjustment
LOANS AND LEASES
Balance at Beginning of Period			(2,200,000)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period			8,900,000
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period			6,600,000
OTHER FINANCIAL ASSETS
Balance at Beginning of Period			400,000
TOTAL
Balance at Beginning of Period			13,700,000
Cumulative Effect Adjustment | Corporate Debt
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period			800,000
Adjusted Balance
LOANS AND LEASES
Balance at Beginning of Period			102,300,000
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period			28,800,000
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period			6,600,000
OTHER FINANCIAL ASSETS
Balance at Beginning of Period			400,000
TOTAL
Balance at Beginning of Period			138,100,000
Adjusted Balance | Corporate Debt
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period			$ 800,000