Allowance for Credit Losses - Loan Balances by Year of Origination and Internally Assigned Risk Rating (Details) - USD ($) $ in Thousands	Jun. 30, 2020		Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 1,004,189
2019	1,260,757
2018	963,963
2017	665,166
2016	701,082
2015 and Prior	1,885,082
Revolving	1,059,103
Revolving-Term	9,216
Total	7,548,558	[1]	$ 7,137,152
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	231,670
2019	477,527
2018	444,368
2017	350,151
2016	431,828
2015 and Prior	872,712
Revolving	53,847
Revolving-Term	0
Total	2,862,103
Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	231,670
2019	468,786
2018	443,243
2017	327,871
2016	401,126
2015 and Prior	769,224
Revolving	48,527
Revolving-Term	0
Total	2,690,447
Commercial real estate | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	8,741
2018	187
2017	13,182
2016	8,172
2015 and Prior	50,717
Revolving	2,350
Revolving-Term	0
Total	83,349
Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	938
2017	9,098
2016	22,059
2015 and Prior	49,912
Revolving	2,890
Revolving-Term	0
Total	84,897
Commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	471
2015 and Prior	2,859
Revolving	80
Revolving-Term	0
Total	3,410
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	351,004
2019	243,588
2018	169,080
2017	104,375
2016	63,338
2015 and Prior	322,811
Revolving	428,436
Revolving-Term	44
Total	1,682,676
Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	350,890
2019	224,067
2018	162,559
2017	88,479
2016	56,286
2015 and Prior	301,155
Revolving	383,176
Revolving-Term	44
Total	1,566,656
Commercial and industrial | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	39
2019	14,104
2018	3,722
2017	917
2016	6,977
2015 and Prior	10,302
Revolving	42,199
Revolving-Term	0
Total	78,260
Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	75
2019	5,417
2018	2,799
2017	14,979
2016	75
2015 and Prior	11,354
Revolving	3,061
Revolving-Term	0
Total	37,760
Commercial and industrial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Revolving	0
Revolving-Term	0
Total	0
Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	67,685
2019	206,187
2018	111,508
2017	19,241
2016	17,335
2015 and Prior	19,207
Revolving	11,935
Revolving-Term	0
Total	453,098
Commercial construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	67,685
2019	206,187
2018	107,927
2017	17,499
2016	17,335
2015 and Prior	10,533
Revolving	11,844
Revolving-Term	0
Total	439,010
Commercial construction | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	3,581
2017	0
2016	0
2015 and Prior	5,076
Revolving	91
Revolving-Term	0
Total	8,748
Commercial construction | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	1,742
2016	0
2015 and Prior	3,598
Revolving	0
Revolving-Term	0
Total	5,340
Commercial construction | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Revolving	0
Revolving-Term	0
Total	0
Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
2020	289,837
2019	172,630
2018	147,368
2017	105,944
2016	94,054
2015 and Prior	345,569
Revolving	111,911
Revolving-Term	1,522
Total	1,268,835
Business banking | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	289,837
2019	171,903
2018	142,912
2017	99,586
2016	88,874
2015 and Prior	310,932
Revolving	110,498
Revolving-Term	1,247
Total	1,215,789
Business banking | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	100
2018	1,341
2017	1,742
2016	1,144
2015 and Prior	7,071
Revolving	733
Revolving-Term	69
Total	12,200
Business banking | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	627
2018	3,115
2017	4,616
2016	4,036
2015 and Prior	27,566
Revolving	680
Revolving-Term	206
Total	40,846
Business banking | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Revolving	0
Revolving-Term	0
Total	0
Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	59,273
2019	143,279
2018	82,271
2017	80,015
2016	89,580
2015 and Prior	318,383
Revolving	422,189
Revolving-Term	7,123
Total	1,202,113
Consumer real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	59,273
2019	143,091
2018	81,972
2017	79,203
2016	87,809
2015 and Prior	309,636
Revolving	421,987
Revolving-Term	7,123
Total	1,190,094
Consumer real estate | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	798
2015 and Prior	300
Revolving	0
Revolving-Term	0
Total	1,098
Consumer real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	188
2018	299
2017	812
2016	973
2015 and Prior	8,447
Revolving	202
Revolving-Term	0
Total	10,921
Consumer real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Revolving	0
Revolving-Term	0
Total	0
Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,720
2019	17,546
2018	9,368
2017	5,440
2016	4,947
2015 and Prior	6,400
Revolving	30,785
Revolving-Term	527
Total	79,733
Other consumer | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,720
2019	16,987
2018	9,223
2017	5,323
2016	4,256
2015 and Prior	1,561
Revolving	30,377
Revolving-Term	268
Total	72,715
Other consumer | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Revolving	0
Revolving-Term	0
Total	0
Other consumer | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	559
2018	145
2017	117
2016	691
2015 and Prior	4,839
Revolving	408
Revolving-Term	259
Total	7,018
Other consumer | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	0
Revolving	0
Revolving-Term	0
Total	$ 0

[1] We had 2,360 loans that were modified totaling $1.4 billion under the CARES Act at June 30, 2020. These customers were not considered past due as a result of their delayed payments. Upon exiting the loan modification deferral program, the measurement of loan delinquency will resume where it left off upon entry into the program. Due to the modification program, this delinquency table may not accurately reflect the credit risk associated with these loans.