Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
LOANS AND LEASES
Balance at Beginning of Period	$ 165,400,000	$ 147,200,000	$ 190,700,000	$ 104,500,000
Charge-Offs	0	(400,000)	(400,000)	(2,200,000)
Recoveries	3,200,000	3,000,000.0	4,500,000	4,100,000
Net Recoveries (Charge-Offs)	3,200,000	2,600,000	4,100,000	1,900,000
Provision for Credit Losses	(19,800,000)	60,400,000	(46,000,000.0)	106,000,000.0
Balance at End of Period	148,800,000	210,200,000	148,800,000	210,200,000
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	55,100,000	40,400,000	61,100,000	19,900,000
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Net Recoveries (Charge-Offs)	0	0	0	0
Provision for Credit Losses	(8,600,000)	8,600,000	(14,600,000)	20,200,000
Balance at End of Period	46,500,000	49,000,000.0	46,500,000	49,000,000.0
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	8,600,000	9,500,000	7,300,000	0
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Net Recoveries (Charge-Offs)	0	0	0	0
Provision for Credit Losses	1,900,000	(3,000,000.0)	3,200,000	(100,000)
Balance at End of Period	10,500,000	6,500,000	10,500,000	6,500,000
OTHER FINANCIAL ASSETS
Balance at Beginning of Period	1,700,000	1,100,000	800,000	0
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Net Recoveries (Charge-Offs)	0	0	0	0
Provision for Credit Losses	(500,000)	200,000	400,000	900,000
Balance at End of Period	1,200,000	1,300,000	1,200,000	1,300,000
TOTAL
Balance at Beginning of Period	230,800,000	198,200,000	259,900,000	124,400,000
Charge-Offs	0	(400,000)	(400,000)	(2,200,000)
Recoveries	3,200,000	3,000,000.0	4,500,000	4,100,000
Net Recoveries (Charge-Offs)	3,200,000	2,600,000	4,100,000	1,900,000
Provision for Credit Losses	(27,000,000.0)	66,200,000	(57,000,000.0)	127,000,000.0
Balance at End of Period	207,000,000.0	267,000,000.0	207,000,000.0	267,000,000.0
Corporate Debt
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	1,100,000	2,700,000	800,000	0
Provision for Credit Losses	500,000	(2,200,000)	800,000	(300,000)
Balance at End of Period	1,600,000	500,000	1,600,000	500,000
TOTAL
Provision for Credit Losses	$ 0	(200,000)	0
Cumulative Effect, Period of Adoption, 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
HELD TO MATURITY DEBT SECURITIES
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, Period of Adoption, Adjustment | Corporate Debt
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period				800,000
Adjusted Balance
LOANS AND LEASES
Balance at Beginning of Period		147,200,000	190,700,000	102,300,000
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		$ 40,400,000	$ 61,100,000	28,800,000
HELD TO MATURITY DEBT SECURITIES
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
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period				$ 800,000