Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
LOANS AND LEASES
Balance at Beginning of Period	$ 190,700,000	$ 104,500,000
Charge-Offs	(400,000)	(1,800,000)
Recoveries	1,300,000	1,100,000
Net (Charge-Offs) Recoveries	900,000	(700,000)
Provision for Credit Losses	(26,200,000)	45,600,000
Balance at End of Period	165,400,000	147,200,000
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	61,100,000	19,900,000
Charge-Offs	0	0
Recoveries	0	0
Net (Charge-Offs) Recoveries	0	0
Provision for Credit Losses	(6,000,000.0)	11,600,000
Balance at End of Period	55,100,000	40,400,000
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	7,300,000	0
Charge-Offs	0	0
Recoveries	0	0
Net (Charge-Offs) Recoveries	0	0
Provision for Credit Losses	1,300,000	2,900,000
Balance at End of Period	8,600,000	9,500,000
OTHER FINANCIAL ASSETS
Balance at Beginning of Period	800,000	0
Charge-Offs	0	0
Recoveries	0	0
Net (Charge-Offs) Recoveries	0	0
Provision for Credit Losses	900,000	700,000
Balance at End of Period	1,700,000	1,100,000
TOTAL
Balance at Beginning of Period	259,900,000	124,400,000
Charge-Offs	(400,000)	(1,800,000)
Recoveries	1,300,000	1,100,000
Net (Charge-Offs) Recoveries	900,000	(700,000)
Provision for Credit Losses	(30,000,000.0)	60,800,000
Balance at End of Period	230,800,000	198,200,000
Corporate Debt
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	800,000	0
Provision for Credit Losses	300,000	1,900,000
Balance at End of Period	1,100,000	2,700,000
TOTAL
Provision for Credit Losses	$ 0	200,000
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
Cumulative Effect Adjustment | Commercial and Consumer Portfolio Segment
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