Loans, Allowance for Loan Losses and Credit Quality (ALLL - by category) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss			$ 6,119,185
Summary of changes in allowance for loan losses
Beginning Balance	$ 67,740	$ 64,293
Charge-offs		(559)
Recoveries		406
Provision for credit losses	25,000	1,000
Ending Balance	$ 92,376	65,140
Ending Balance: Individually Evaluated for Impairment		1,104	980
Ending Balance: Collectively Evaluated for Impairment		64,036
Commercial and Industrial [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss			1,395,036
Summary of changes in allowance for loan losses
Beginning Balance		15,760
Charge-offs		0
Recoveries		124
Provision for credit losses		988
Ending Balance		16,872
Ending Balance: Individually Evaluated for Impairment		58	126
Ending Balance: Collectively Evaluated for Impairment		16,814
Commercial Real Estate [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss			4,002,359
Summary of changes in allowance for loan losses
Beginning Balance		32,370
Charge-offs		0
Recoveries		33
Provision for credit losses		(354)
Ending Balance		32,049
Ending Balance: Individually Evaluated for Impairment		75	48
Ending Balance: Collectively Evaluated for Impairment		31,974
Construction Loans [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss			547,293
Summary of changes in allowance for loan losses
Beginning Balance		5,158
Charge-offs		0
Recoveries		0
Provision for credit losses		197
Ending Balance		5,355
Ending Balance: Individually Evaluated for Impairment		0
Ending Balance: Collectively Evaluated for Impairment		5,355
Small Business [Member]
Financing Receivable Impaired [Line Items]
Financing Receivable, after Allowance for Credit Loss			174,497
Summary of changes in allowance for loan losses
Beginning Balance		1,756
Charge-offs		(145)
Recoveries		27
Provision for credit losses		146
Ending Balance		1,784
Ending Balance: Individually Evaluated for Impairment		1	8
Ending Balance: Collectively Evaluated for Impairment		1,783
Residential Real Estate [Member]
Summary of changes in allowance for loan losses
Beginning Balance		3,219
Charge-offs		0
Recoveries		1
Provision for credit losses		14
Ending Balance		3,234
Ending Balance: Individually Evaluated for Impairment		802	637
Ending Balance: Collectively Evaluated for Impairment		2,432
Consumer Home Equity [Member]
Summary of changes in allowance for loan losses
Beginning Balance		5,608
Charge-offs		(113)
Recoveries		66
Provision for credit losses		(54)
Ending Balance		5,507
Ending Balance: Individually Evaluated for Impairment		161	156
Ending Balance: Collectively Evaluated for Impairment		5,346
Consumer - Other [Member]
Summary of changes in allowance for loan losses
Beginning Balance		422
Charge-offs		(301)
Recoveries		155
Provision for credit losses		63
Ending Balance		339
Ending Balance: Individually Evaluated for Impairment		7	5
Ending Balance: Collectively Evaluated for Impairment		$ 332
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