Allowance for Credit Losses - Loan Balances by Year of Origination and Performing and Nonperforming Status (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 1,360,684
2019	1,214,746
2018	831,734
2017	565,201
2016	610,556
2015 and Prior	1,572,826
Revolving	1,041,199
Revolving-Term	28,914
Total	7,225,860		$ 7,137,152
Performing TDRs
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,360,654
2019	1,196,491
2018	827,625
2017	543,253
2016	586,622
2015 and Prior	1,496,135
Revolving	1,040,544
Revolving-Term	27,762
Total	7,079,086
Nonperforming TDRs
Financing Receivable, Credit Quality Indicator [Line Items]
2020	30
2019	18,254
2018	4,108
2017	21,948
2016	23,934
2015 and Prior	76,691
Revolving	654
Revolving-Term	1,153
Total	146,774
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	5,977,643		5,756,971
Commercial | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	334,086
2019	476,203
2018	417,944
2017	320,140
2016	415,184
2015 and Prior	780,560
Revolving	47,830
Revolving-Term	0
Total	2,791,947	$ 3,416,518	3,059,592
Commercial | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	457,828
2019	215,457
2018	145,290
2017	82,249
2016	28,488
2015 and Prior	221,609
Revolving	408,631
Revolving-Term	0
Total	1,559,552	1,720,833	1,480,529
Commercial | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	132,813
2019	230,907
2018	63,535
2017	2,921
2016	6,346
2015 and Prior	16,777
Revolving	12,778
Revolving-Term	0
Total	466,077	375,445	370,060
Commercial | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
2020	296,357
2019	156,473
2018	128,250
2017	91,363
2016	82,202
2015 and Prior	298,779
Revolving	105,549
Revolving-Term	1,094
Total	1,160,067	0	846,790
Commercial | Performing TDRs | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	334,086
2019	459,799
2018	417,944
2017	313,465
2016	394,972
2015 and Prior	722,782
Revolving	47,830
Revolving-Term	0
Total	2,690,879
Commercial | Performing TDRs | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	457,828
2019	214,144
2018	143,706
2017	69,411
2016	28,426
2015 and Prior	220,701
Revolving	408,350
Revolving-Term	0
Total	1,542,566
Commercial | Performing TDRs | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	132,813
2019	230,907
2018	63,535
2017	2,921
2016	6,346
2015 and Prior	16,393
Revolving	12,778
Revolving-Term	0
Total	465,692
Commercial | Performing TDRs | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
2020	296,327
2019	156,164
2018	126,432
2017	90,414
2016	80,106
2015 and Prior	286,970
Revolving	105,494
Revolving-Term	1,037
Total	1,142,944
Commercial | Nonperforming TDRs | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	16,404
2018	0
2017	6,675
2016	20,212
2015 and Prior	57,778
Revolving	0
Revolving-Term	0
Total	101,070
Commercial | Nonperforming TDRs | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	1,313
2018	1,584
2017	12,838
2016	62
2015 and Prior	908
Revolving	281
Revolving-Term	0
Total	16,985
Commercial | Nonperforming TDRs | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	384
Revolving	0
Revolving-Term	0
Total	384
Commercial | Nonperforming TDRs | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
2020	30
2019	309
2018	1,818
2017	949
2016	2,096
2015 and Prior	11,809
Revolving	55
Revolving-Term	57
Total	17,123
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,248,217		1,380,181
Consumer | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total			8,390
Consumer | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	120,736
2019	122,544
2018	69,931
2017	65,133
2016	76,254
2015 and Prior	251,047
Revolving	439,020
Revolving-Term	22,667
Total	1,167,332	1,545,323	1,295,207
Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	18,864
2019	13,162
2018	6,784
2017	3,395
2016	2,082
2015 and Prior	4,054
Revolving	27,391
Revolving-Term	5,153
Total	80,885	$ 79,033	$ 84,974
Consumer | Performing TDRs | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	120,736
2019	122,315
2018	69,225
2017	63,647
2016	74,690
2015 and Prior	245,331
Revolving	438,702
Revolving-Term	21,572
Total	1,156,216
Consumer | Performing TDRs | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	18,864
2019	13,162
2018	6,784
2017	3,395
2016	2,082
2015 and Prior	3,958
Revolving	27,391
Revolving-Term	5,153
Total	80,789
Consumer | Nonperforming TDRs | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	229
2018	706
2017	1,486
2016	1,564
2015 and Prior	5,716
Revolving	318
Revolving-Term	1,096
Total	11,116
Consumer | Nonperforming TDRs | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 and Prior	96
Revolving	0
Revolving-Term	0
Total	$ 96