Allowance for Credit Losses - Loan Balances by Year of Origination and Internally Assigned Risk Rating (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
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 | Pass | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	334,086
2019	422,800
2018	394,963
2017	277,724
2016	307,321
2015 and Prior	615,217
Revolving	46,330
Revolving-Term	0
Total	2,398,441
Commercial | Pass | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	454,131
2019	199,453
2018	140,049
2017	68,607
2016	27,645
2015 and Prior	206,782
Revolving	383,082
Revolving-Term	0
Total	1,479,749
Commercial | Pass | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	131,235
2019	224,794
2018	59,649
2017	2,420
2016	6,346
2015 and Prior	4,555
Revolving	12,778
Revolving-Term	0
Total	441,777
Commercial | Pass | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
2020	296,254
2019	154,335
2018	123,207
2017	86,552
2016	77,238
2015 and Prior	266,042
Revolving	103,571
Revolving-Term	291
Total	1,107,490
Commercial | Special mention | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	35,499
2018	10,200
2017	22,502
2016	55,174
2015 and Prior	75,022
Revolving	0
Revolving-Term	0
Total	198,397
Commercial | Special mention | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,697
2019	8,211
2018	2,628
2017	697
2016	768
2015 and Prior	1,046
Revolving	23,527
Revolving-Term	0
Total	40,574
Commercial | Special mention | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,578
2019	2,533
2018	3,886
2017	0
2016	0
2015 and Prior	8,593
Revolving	0
Revolving-Term	0
Total	16,590
Commercial | Special mention | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	1,060
2018	1,147
2017	1,602
2016	1,084
2015 and Prior	6,866
Revolving	637
Revolving-Term	123
Total	12,519
Commercial | Substandard | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	17,259
2018	12,781
2017	19,914
2016	50,700
2015 and Prior	83,792
Revolving	1,500
Revolving-Term	0
Total	185,946
Commercial | Substandard | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	7,793
2018	2,613
2017	8,544
2016	75
2015 and Prior	13,781
Revolving	2,022
Revolving-Term	0
Total	34,828
Commercial | Substandard | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	3,580
2018	0
2017	501
2016	0
2015 and Prior	3,629
Revolving	0
Revolving-Term	0
Total	7,710
Commercial | Substandard | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
2020	103
2019	1,078
2018	3,896
2017	3,209
2016	3,880
2015 and Prior	25,871
Revolving	1,341
Revolving-Term	680
Total	40,058
Commercial | Doubtful | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	645
2018	0
2017	0
2016	1,989
2015 and Prior	6,529
Revolving	0
Revolving-Term	0
Total	9,163
Commercial | Doubtful | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	4,401
2016	0
2015 and Prior	0
Revolving	0
Revolving-Term	0
Total	4,401
Commercial | Doubtful | Commercial construction
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 | Doubtful | Business banking
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
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 | Pass | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	120,736
2019	122,171
2018	67,700
2017	63,653
2016	73,805
2015 and Prior	243,939
Revolving	438,888
Revolving-Term	22,667
Total	1,153,559
Consumer | Pass | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	18,849
2019	13,162
2018	6,784
2017	3,395
2016	2,082
2015 and Prior	687
Revolving	26,647
Revolving-Term	2,767
Total	74,373
Consumer | Special mention | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	1,489
2017	0
2016	0
2015 and Prior	150
Revolving	132
Revolving-Term	0
Total	1,771
Consumer | Special mention | Other consumer
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 | Substandard | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	373
2018	742
2017	1,480
2016	2,449
2015 and Prior	6,958
Revolving	0
Revolving-Term	0
Total	12,002
Consumer | Substandard | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	15
2019	0
2018	0
2017	0
2016	0
2015 and Prior	3,367
Revolving	744
Revolving-Term	2,386
Total	6,512
Consumer | Doubtful | Consumer real estate
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 | Doubtful | Other consumer
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