Allowance for Credit Losses - Loan Balances by Year of Origination and Internally Assigned Risk Rating (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	$ 1,035,267	$ 1,360,684
Year two	854,925	1,214,746
Year three	1,107,652	831,734
Year four	688,325	565,201
Year five	462,114	610,556
More than five years	1,692,697	1,572,826
Revolving	1,100,863	1,041,199
Revolving-Term	28,244	28,914
Total	6,970,087	7,225,860
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,029,863	1,355,292
Year two	847,760	1,136,716
Year three	1,017,394	792,352
Year four	653,430	502,350
Year five	394,438	494,436
More than five years	1,416,288	1,337,222
Revolving	1,081,538	1,011,297
Revolving-Term	24,651	25,724
Total	6,465,362	6,655,389
Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	162	5,274
Year two	4,448	47,302
Year three	34,953	19,350
Year four	8,994	24,802
Year five	39,973	57,026
More than five years	112,175	91,677
Revolving	10,866	24,296
Revolving-Term	121	124
Total	211,692	269,851
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	5,242	118
Year two	2,717	30,083
Year three	45,441	20,032
Year four	25,901	33,648
Year five	27,703	57,105
More than five years	164,234	137,398
Revolving	8,459	5,606
Revolving-Term	3,472	3,066
Total	283,169	287,056
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	0	645
Year three	9,864	0
Year four	0	4,401
Year five	0	1,989
More than five years	0	6,529
Revolving	0	0
Revolving-Term	0	0
Total	9,864	13,564
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	5,423,964	5,673,707
Commercial | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	255,876	334,086
Year two	325,327	476,203
Year three	493,611	417,944
Year four	365,129	320,140
Year five	281,897	415,184
More than five years	937,114	780,560
Revolving	43,826	47,830
Revolving-Term	0	0
Total	2,702,780	2,791,947
Commercial | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	406,445	457,828
Year two	159,516	215,457
Year three	175,718	145,290
Year four	102,677	82,249
Year five	48,349	28,488
More than five years	141,411	221,609
Revolving	444,082	408,631
Revolving-Term		0
Total	1,478,198	1,559,552
Commercial | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	100,774	132,813
Year two	136,589	230,907
Year three	179,924	63,535
Year four	33,903	2,921
Year five	996	6,346
More than five years	12,024	16,777
Revolving	21,714	12,778
Revolving-Term		0
Total	485,924	466,077
Commercial | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	173,313	296,357
Year two	115,055	156,473
Year three	155,033	128,250
Year four	122,227	91,363
Year five	84,905	82,202
More than five years	344,047	298,779
Revolving	104,339	105,549
Revolving-Term	1,206	1,094
Total	1,100,125	1,160,067
Commercial | Pass | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	255,876	334,086
Year two	323,514	422,800
Year three	443,487	394,963
Year four	341,387	277,724
Year five	224,258	307,321
More than five years	716,460	615,217
Revolving	42,326	46,330
Revolving-Term	0	0
Total	2,347,308	2,398,441
Commercial | Pass | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	401,200	454,131
Year two	156,589	199,453
Year three	145,923	140,049
Year four	98,137	68,607
Year five	43,019	27,645
More than five years	133,945	206,782
Revolving	428,398	383,082
Revolving-Term	0	0
Total	1,407,211	1,479,749
Commercial | Pass | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	100,774	131,235
Year two	134,440	224,794
Year three	172,508	59,649
Year four	33,903	2,420
Year five	996	6,346
More than five years	4,298	4,555
Revolving	21,714	12,778
Revolving-Term	0	0
Total	468,633	441,777
Commercial | Pass | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	173,154	296,254
Year two	114,831	154,335
Year three	152,423	123,207
Year four	117,529	86,552
Year five	81,934	77,238
More than five years	316,445	266,042
Revolving	103,162	103,571
Revolving-Term	450	291
Total	1,059,928	1,107,490
Commercial | Special mention | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	1,368	35,499
Year three	32,780	10,200
Year four	4,422	22,502
Year five	38,966	55,174
More than five years	97,322	75,022
Revolving	0	0
Revolving-Term		0
Total	174,858	198,397
Commercial | Special mention | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	49	3,697
Year two	2,927	8,211
Year three	1,283	2,628
Year four	3,166	697
Year five	72	768
More than five years	1,934	1,046
Revolving	10,667	23,527
Revolving-Term		0
Total	20,098	40,574
Commercial | Special mention | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	1,578
Year two	0	2,533
Year three	0	3,886
Year four	0	0
Year five	0	0
More than five years	4,491	8,593
Revolving	0	0
Revolving-Term		0
Total	4,491	16,590
Commercial | Special mention | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	113	0
Year two	153	1,060
Year three	890	1,147
Year four	1,406	1,602
Year five	935	1,084
More than five years	6,265	6,866
Revolving	199	637
Revolving-Term	121	123
Total	10,082	12,519
Commercial | Substandard | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	445	17,259
Year three	16,812	12,781
Year four	19,320	19,914
Year five	18,673	50,700
More than five years	123,332	83,792
Revolving	1,500	1,500
Revolving-Term		0
Total	180,082	185,946
Commercial | Substandard | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	5,196	0
Year two	0	7,793
Year three	19,180	2,613
Year four	1,374	8,544
Year five	5,258	75
More than five years	5,532	13,781
Revolving	5,017	2,022
Revolving-Term		0
Total	41,557	34,828
Commercial | Substandard | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	2,149	3,580
Year three	7,416	0
Year four	0	501
Year five	0	0
More than five years	3,235	3,629
Revolving	0	0
Revolving-Term		0
Total	12,800	7,710
Commercial | Substandard | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	46	103
Year two	71	1,078
Year three	1,720	3,896
Year four	3,292	3,209
Year five	2,036	3,880
More than five years	21,337	25,871
Revolving	978	1,341
Revolving-Term	635	680
Total	30,115	40,058
Commercial | Doubtful | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	0	645
Year three	532	0
Year four	0	0
Year five	0	1,989
More than five years	0	6,529
Revolving	0	0
Revolving-Term	0	0
Total	532	9,163
Commercial | Doubtful | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	0	0
Year three	9,332	0
Year four	0	4,401
Year five	0	0
More than five years	0	0
Revolving	0	0
Revolving-Term	0	0
Total	9,332	4,401
Commercial | Doubtful | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	0	0
Year three	0	0
Year four	0	0
Year five	0	0
More than five years	0	0
Revolving	0	0
Revolving-Term	0	0
Total	0	0
Commercial | Doubtful | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	0	0
Year three	0	0
Year four	0	0
Year five	0	0
More than five years	0	0
Revolving	0	0
Revolving-Term	0	0
Total	0	0
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,546,123	1,552,153
Consumer | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Total		303,900
Consumer | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	89,026	120,736
Year two	107,534	122,544
Year three	94,791	69,931
Year four	60,387	65,133
Year five	44,157	76,254
More than five years	249,283	251,047
Revolving	435,922	439,020
Revolving-Term	24,378	22,667
Total	1,105,478	1,167,332
Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	9,833	18,864
Year two	10,904	13,162
Year three	8,575	6,784
Year four	4,002	3,395
Year five	1,810	2,082
More than five years	8,818	4,054
Revolving	50,980	27,391
Revolving-Term	2,660	5,153
Total	97,582	80,885
Consumer | Pass | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	89,026	120,736
Year two	107,534	122,171
Year three	94,583	67,700
Year four	58,622	63,653
Year five	42,789	73,805
More than five years	242,252	243,939
Revolving	435,213	438,888
Revolving-Term	23,088	22,667
Total	1,093,107	1,153,559
Consumer | Pass | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	9,833	18,849
Year two	10,852	13,162
Year three	8,470	6,784
Year four	3,852	3,395
Year five	1,442	2,082
More than five years	2,888	687
Revolving	50,725	26,647
Revolving-Term	1,113	2,767
Total	89,175	74,373
Consumer | Special mention | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	0	0
Year three	0	1,489
Year four	0	0
Year five	0	0
More than five years	2,163	150
Revolving	0	132
Revolving-Term		0
Total	2,163	1,771
Consumer | Special mention | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	0	0
Year three	0	0
Year four	0	0
Year five	0	0
More than five years	0	0
Revolving	0	0
Revolving-Term	0	0
Total	0	0
Consumer | Substandard | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	0	373
Year three	208	742
Year four	1,765	1,480
Year five	1,368	2,449
More than five years	4,868	6,958
Revolving	709	0
Revolving-Term	1,290	0
Total	10,208	12,002
Consumer | Substandard | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	15
Year two	52	0
Year three	105	0
Year four	150	0
Year five	368	0
More than five years	5,930	3,367
Revolving	255	744
Revolving-Term	1,547	2,386
Total	8,407	6,512
Consumer | Doubtful | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	0	0
Year three	0	0
Year four	0	0
Year five	0	0
More than five years	0	0
Revolving	0	0
Revolving-Term	0	0
Total	0	0
Consumer | Doubtful | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Year two	0	0
Year three	0	0
Year four	0	0
Year five	0	0
More than five years	0	0
Revolving	0	0
Revolving-Term	0	0
Total	$ 0	$ 0