Loan Portfolio and Credit Quality - Loans by Grade or Nonaccrual Status (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	$ 352,128	$ 1,446,964
Last fiscal year	1,368,099	1,171,069
Two years prior	1,141,864	787,841
Three years prior	744,578	784,080
Four years prior	736,998	889,143
Prior	2,241,728	1,460,828
Revolving	586,541	515,053
Revolving Converted to Term	44,389	49,331
Net loans	7,216,325	7,104,309
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	27,437	97,772
Last fiscal year	94,437	83,726
Two years prior	77,081	73,111
Three years prior	65,497	14,052
Four years prior	13,009	18,785
Prior	60,548	46,404
Revolving	313,367	204,858
Revolving Converted to Term	16,841	19,635
Net loans	668,217	558,343
Paycheck Protection Program
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	113,041	312,356
Last fiscal year	238,129	0
Two years prior	0	0
Three years prior	0	0
Four years prior	0	0
Prior	0	0
Revolving	0	0
Revolving Converted to Term	0	0
Net loans	351,170	312,356
Commercial tax-exempt
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	53,225
Last fiscal year	89,135	20,586
Two years prior	38,215	40,451
Three years prior	40,285	24,624
Four years prior	24,410	102,133
Prior	293,471	198,107
Revolving	0	0
Revolving Converted to Term	2,991	3,033
Net loans	488,507	442,159
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	65,639	336,427
Last fiscal year	288,267	530,844
Two years prior	515,423	273,610
Three years prior	275,268	337,898
Four years prior	332,445	412,836
Prior	1,115,638	722,977
Revolving	90,526	126,593
Revolving Converted to Term	14,471	16,190
Net loans	2,697,677	2,757,375
Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	6,774	43,042
Last fiscal year	57,925	63,914
Two years prior	73,762	33,730
Three years prior	24,531	16,288
Four years prior	16,262	2,230
Prior	2,228	0
Revolving	0	0
Revolving Converted to Term	0	0
Net loans	181,482	159,204
Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	138,273	603,414
Last fiscal year	599,553	471,841
Two years prior	437,236	366,662
Three years prior	338,978	391,218
Four years prior	350,872	352,392
Prior	767,627	491,937
Revolving	0	0
Revolving Converted to Term	15	0
Net loans	2,632,554	2,677,464
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	0
Two years prior	0	252
Three years prior	0	0
Four years prior	0	686
Prior	1,623	829
Revolving	60,058	65,124
Revolving Converted to Term	10,071	10,473
Net loans	71,752	77,364
Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	964	728
Last fiscal year	653	158
Two years prior	147	25
Three years prior	19	0
Four years prior	0	81
Prior	593	574
Revolving	122,590	118,478
Revolving Converted to Term	0	0
Net loans	124,966	120,044
Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	5,957
Two years prior	6,190	622
Three years prior	819	2,373
Four years prior	2,987	875
Prior	12,185	10,759
Revolving	1,085	1,201
Revolving Converted to Term	2,498	2,064
Net loans	25,764	23,851
Nonaccrual Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	141
Two years prior	375	350
Three years prior	346	0
Four years prior	16	813
Prior	903	14
Revolving	884	1,012
Revolving Converted to Term	2,242	2,064
Net loans	4,766	4,394
Nonaccrual Loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	5,212
Two years prior	5,212	0
Three years prior	0	0
Four years prior	598	0
Prior	0	0
Revolving	49	49
Revolving Converted to Term	0	0
Net loans	5,859	5,261
Nonaccrual Loans | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	604
Two years prior	603	272
Three years prior	473	2,373
Four years prior	2,373	62
Prior	11,026	10,469
Revolving	0	0
Revolving Converted to Term	0	0
Net loans	14,475	13,780
Nonaccrual Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	0
Two years prior	0	0
Three years prior	0	0
Four years prior	0	0
Prior	256	276
Revolving	139	139
Revolving Converted to Term	256	0
Net loans	651	415
Nonaccrual Loans | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	0
Two years prior	0	0
Three years prior	0	0
Four years prior	0	0
Prior	0	0
Revolving	13	1
Revolving Converted to Term	0	0
Net loans	13	1
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	347,528	1,420,600
Last fiscal year	1,341,947	1,098,988
Two years prior	1,065,066	751,286
Three years prior	707,304	751,572
Four years prior	702,821	851,145
Prior	2,127,914	1,371,548
Revolving	573,683	500,958
Revolving Converted to Term	35,696	40,241
Net loans	6,901,959	6,786,338
Pass | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	22,837	96,230
Last fiscal year	92,124	80,949
Two years prior	71,592	65,506
Three years prior	57,958	13,378
Four years prior	12,334	17,972
Prior	56,994	43,592
Revolving	301,010	191,252
Revolving Converted to Term	8,404	10,801
Net loans	623,253	519,680
Pass | Paycheck Protection Program
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	113,041	312,356
Last fiscal year	238,129	0
Two years prior	0	0
Three years prior	0	0
Four years prior	0	0
Prior	0	0
Revolving	0	0
Revolving Converted to Term	0	0
Net loans	351,170	312,356
Pass | Commercial tax-exempt
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	53,225
Last fiscal year	89,135	20,586
Two years prior	38,215	40,451
Three years prior	40,285	24,624
Four years prior	24,410	102,133
Prior	290,684	190,798
Revolving	0	0
Revolving Converted to Term	2,991	3,033
Net loans	485,720	434,850
Pass | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	65,639	311,605
Last fiscal year	264,428	462,144
Two years prior	444,717	247,228
Three years prior	248,987	308,437
Four years prior	301,316	375,713
Prior	1,022,447	657,563
Revolving	90,477	126,544
Revolving Converted to Term	14,471	16,190
Net loans	2,452,482	2,505,424
Pass | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	6,774	43,042
Last fiscal year	57,925	63,914
Two years prior	73,762	31,434
Three years prior	21,550	16,288
Four years prior	16,262	2,230
Prior	2,228	0
Revolving	0	0
Revolving Converted to Term	0	0
Net loans	178,501	156,908
Pass | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	138,273	603,414
Last fiscal year	599,553	471,237
Two years prior	436,633	366,390
Three years prior	338,505	388,845
Four years prior	348,499	352,330
Prior	753,601	478,468
Revolving	0	0
Revolving Converted to Term	15	0
Net loans	2,615,079	2,660,684
Pass | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	0
Two years prior	0	252
Three years prior	0	0
Four years prior	0	686
Prior	1,367	553
Revolving	59,919	64,985
Revolving Converted to Term	9,815	10,217
Net loans	71,101	76,693
Pass | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	964	728
Last fiscal year	653	158
Two years prior	147	25
Three years prior	19	0
Four years prior	0	81
Prior	593	574
Revolving	122,277	118,177
Revolving Converted to Term	0	0
Net loans	124,653	119,743
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	22,019
Last fiscal year	18,574	16,264
Two years prior	20,832	15,686
Three years prior	6,250	30,135
Four years prior	17,744	37,123
Prior	84,757	61,537
Revolving	4,064	4,211
Revolving Converted to Term	251	262
Net loans	152,472	187,237
Special Mention | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	358
Last fiscal year	321	2,413
Two years prior	4,919	1,008
Three years prior	952	674
Four years prior	0	0
Prior	2,588	2,688
Revolving	3,764	3,911
Revolving Converted to Term	251	262
Net loans	12,795	11,314
Special Mention | Commercial tax-exempt
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	0
Two years prior	0	0
Three years prior	0	0
Four years prior	0	0
Prior	2,787	2,806
Revolving	0	0
Revolving Converted to Term	0	0
Net loans	2,787	2,806
Special Mention | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	21,661
Last fiscal year	18,253	13,851
Two years prior	15,913	12,382
Three years prior	2,317	29,461
Four years prior	17,744	37,123
Prior	79,382	56,043
Revolving	0	0
Revolving Converted to Term	0	0
Net loans	133,609	170,521
Special Mention | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	0
Two years prior	0	2,296
Three years prior	2,981	0
Four years prior	0	0
Prior	0	0
Revolving	0	0
Revolving Converted to Term	0	0
Net loans	2,981	2,296
Special Mention | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	0
Two years prior	0	0
Three years prior	0	0
Four years prior	0	0
Prior	0	0
Revolving	300	300
Revolving Converted to Term	0	0
Net loans	300	300
Accruing Classified
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	4,600	4,345
Last fiscal year	7,578	49,860
Two years prior	49,776	20,247
Three years prior	30,205	0
Four years prior	13,446	0
Prior	16,872	16,984
Revolving	7,709	8,683
Revolving Converted to Term	5,944	6,764
Net loans	136,130	106,883
Accruing Classified | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	4,600	1,184
Last fiscal year	1,992	223
Two years prior	195	6,247
Three years prior	6,241	0
Four years prior	659	0
Prior	63	110
Revolving	7,709	8,683
Revolving Converted to Term	5,944	6,508
Net loans	27,403	22,955
Accruing Classified | Commercial tax-exempt
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0
Last fiscal year		0
Two years prior		0
Three years prior		0
Four years prior		0
Prior		4,503
Revolving		0
Revolving Converted to Term		0
Net loans		4,503
Accruing Classified | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	3,161
Last fiscal year	5,586	49,637
Two years prior	49,581	14,000
Three years prior	23,964	0
Four years prior	12,787	0
Prior	13,809	9,371
Revolving	0	0
Revolving Converted to Term	0	0
Net loans	105,727	76,169
Accruing Classified | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Last fiscal year	0	0
Two years prior	0	0
Three years prior	0	0
Four years prior	0	0
Prior	3,000	3,000
Revolving	0	0
Revolving Converted to Term	0	0
Net loans	3,000	3,000
Accruing Classified | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0
Last fiscal year		0
Two years prior		0
Three years prior		0
Four years prior		0
Prior		0
Revolving		0
Revolving Converted to Term		256
Net loans		256
Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Net loans	25,764	23,851
Accruing Classified | Nonaccrual Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Net loans	4,766	4,394
Accruing Classified | Nonaccrual Loans | Paycheck Protection Program
Financing Receivable, Credit Quality Indicator [Line Items]
Net loans	0	0
Accruing Classified | Nonaccrual Loans | Commercial tax-exempt
Financing Receivable, Credit Quality Indicator [Line Items]
Net loans	0	0
Accruing Classified | Nonaccrual Loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Net loans	5,859	5,261
Accruing Classified | Nonaccrual Loans | Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
Net loans	0	0
Accruing Classified | Nonaccrual Loans | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Net loans	14,475	13,780
Accruing Classified | Nonaccrual Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Net loans	651	415
Accruing Classified | Nonaccrual Loans | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
Net loans	$ 13	$ 1