Loans, Allowance for Loan Losses and Credit Quality (ALLL - by category) (Details) - USD ($) $ in Thousands	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
Financing Receivable Impaired [Line Items]
Financing Receivable, Collectively Evaluated for Impairment							$ 8,809,155
Financing Receivable, Individually Evaluated for Impairment							49,628
Financing Receivable, after Allowance for Credit Loss							6,119,185
Summary of changes in allowance for loan losses
Beginning Balance			$ 67,740	$ 65,960	$ 67,740	$ 64,293
Charge-offs				707		(1,738)
Recoveries				1,689		2,387
Provision for credit losses	$ 7,500	$ 20,000	$ 25,000	0	52,500	2,000
Ending Balance	115,625			66,942	115,625	66,942
Ending Balance: Individually Evaluated for Impairment	837				837		980
Ending Balance: Collectively Evaluated for Impairment	66,105				66,105
Loans and Leases Receivable, Gross	9,405,193				9,405,193		8,873,639
Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, Collectively Evaluated for Impairment							1,370,580
Financing Receivable, Individually Evaluated for Impairment							24,456
Financing Receivable, after Allowance for Credit Loss							1,395,036
Summary of changes in allowance for loan losses
Beginning Balance				16,857		15,760
Charge-offs				0		0
Recoveries				1,003		1,127
Provision for credit losses				(528)		445
Ending Balance	17,332				17,332
Ending Balance: Individually Evaluated for Impairment	6				6		126
Ending Balance: Collectively Evaluated for Impairment	17,326				17,326
Financing Receivable, before Allowance for Credit Loss	2,062,345				2,062,345		1,395,036
Loans and Leases Receivable, Gross	2,062,345				2,062,345		1,395,036
Commercial Real Estate [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, Collectively Evaluated for Impairment							3,987,848
Financing Receivable, Individually Evaluated for Impairment							8,337
Financing Receivable, after Allowance for Credit Loss							4,002,359
Summary of changes in allowance for loan losses
Beginning Balance				32,660		32,370
Charge-offs				82		(82)
Recoveries				106		152
Provision for credit losses				(33)		211
Ending Balance	32,651				32,651
Ending Balance: Individually Evaluated for Impairment	41				41		48
Ending Balance: Collectively Evaluated for Impairment	32,610				32,610
Financing Receivable, before Allowance for Credit Loss	4,125,464				4,125,464		4,002,359
Loans and Leases Receivable, Gross	4,125,464				4,125,464		4,002,359
Construction Loans [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, Collectively Evaluated for Impairment							547,293
Financing Receivable, Individually Evaluated for Impairment							0
Financing Receivable, after Allowance for Credit Loss							547,293
Summary of changes in allowance for loan losses
Beginning Balance				5,593		5,158
Charge-offs				0		0
Recoveries				0		0
Provision for credit losses				240		675
Ending Balance	5,833				5,833
Ending Balance: Individually Evaluated for Impairment	0				0
Ending Balance: Collectively Evaluated for Impairment	5,833				5,833
Financing Receivable, before Allowance for Credit Loss	573,334				573,334		547,293
Loans and Leases Receivable, Gross	573,334				573,334		547,293
Small Business [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, Collectively Evaluated for Impairment							173,960
Financing Receivable, Individually Evaluated for Impairment							537
Financing Receivable, after Allowance for Credit Loss							174,497
Summary of changes in allowance for loan losses
Beginning Balance				1,768		1,756
Charge-offs				125		(319)
Recoveries				61		108
Provision for credit losses				48		207
Ending Balance	1,752				1,752
Ending Balance: Individually Evaluated for Impairment	11				11		8
Ending Balance: Collectively Evaluated for Impairment	1,741				1,741
Financing Receivable, before Allowance for Credit Loss	167,632				167,632		174,497
Loans and Leases Receivable, Gross	167,632				167,632		174,497
Residential Real Estate [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, Collectively Evaluated for Impairment							1,571,848
Financing Receivable, Individually Evaluated for Impairment							11,228
Summary of changes in allowance for loan losses
Beginning Balance				3,296		3,219
Charge-offs				0		0
Recoveries				140		141
Provision for credit losses				(88)		(12)
Ending Balance	3,348				3,348
Ending Balance: Individually Evaluated for Impairment	619				619		637
Ending Balance: Collectively Evaluated for Impairment	2,729				2,729
Financing Receivable, before Allowance for Credit Loss	1,352,305				1,352,305		1,590,569
Loans and Leases Receivable, Gross	1,352,305				1,352,305		1,590,569
Consumer Home Equity [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, Collectively Evaluated for Impairment							1,127,963
Financing Receivable, Individually Evaluated for Impairment							4,948
Summary of changes in allowance for loan losses
Beginning Balance				5,547		5,608
Charge-offs				28		(212)
Recoveries				194		278
Provision for credit losses				36		75
Ending Balance	5,749				5,749
Ending Balance: Individually Evaluated for Impairment	155				155		156
Ending Balance: Collectively Evaluated for Impairment	5,594				5,594
Loans and Leases Receivable, Gross	1,101,054				1,101,054		1,133,798
Consumer - Other [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, Collectively Evaluated for Impairment							29,663
Financing Receivable, Individually Evaluated for Impairment							122
Summary of changes in allowance for loan losses
Beginning Balance				239		422
Charge-offs				472		(1,125)
Recoveries				185		581
Provision for credit losses				$ 325		$ 399
Ending Balance	277				277
Ending Balance: Individually Evaluated for Impairment	5				5		5
Ending Balance: Collectively Evaluated for Impairment	272				272
Financing Receivable, before Allowance for Credit Loss	23,059				23,059		30,087
Loans and Leases Receivable, Gross	$ 23,059				$ 23,059		30,087	[1]
Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss							14,856
Financial Asset Acquired with Credit Deterioration [Member] | Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss							0
Financial Asset Acquired with Credit Deterioration [Member] | Commercial Real Estate [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss							6,174
Financial Asset Acquired with Credit Deterioration [Member] | Construction Loans [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss							0
Financial Asset Acquired with Credit Deterioration [Member] | Small Business [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss							0
Financial Asset Acquired with Credit Deterioration [Member] | Residential Real Estate [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss							7,493
Financial Asset Acquired with Credit Deterioration [Member] | Consumer Home Equity [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss							887
Financial Asset Acquired with Credit Deterioration [Member] | Consumer - Other [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss							$ 302

[1] Other consumer portfolio is inclusive of deposit account overdrafts recorded as loan balances.