Loan Portfolio and Credit Quality - Loans by Grade or Nonaccrual Status (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 955,735
2019	1,292,099
2018	942,497
2017	911,800
2016	1,031,046
Prior	1,702,123
Revolving	497,654
Total Loans Receivable	7,332,954	$ 6,976,704
Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	49
2019	5,708
2018	1,157
2017	2,726
2016	0
Prior	12,589
Revolving	3,375
Total Loans Receivable	25,604
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	933,594
2019	1,235,090
2018	900,975
2017	886,965
2016	983,106
Prior	1,607,177
Revolving	479,975
Total Loans Receivable	7,026,882
Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	7,026,882	6,850,653
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	20,640
2019	35,342
2018	32,910
2017	2,229
2016	37,704
Prior	60,044
Revolving	3,013
Total Loans Receivable	191,882
Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	191,882	52,026
Accruing Classified
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,452
2019	15,959
2018	7,455
2017	19,880
2016	10,236
Prior	22,313
Revolving	11,291
Total Loans Receivable	88,586
Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	25,604	16,103
Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	88,586	57,922
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	24,289
2019	98,101
2018	81,275
2017	33,133
2016	27,059
Prior	60,807
Revolving	241,084
Total Loans Receivable	565,748	694,034
Commercial and industrial | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	49
2019	161
2018	0
2017	197
2016	0
Prior	14
Revolving	3,228
Total Loans Receivable	3,649
Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	24,040
2019	92,841
2018	72,857
2017	16,771
2016	25,701
Prior	57,514
Revolving	223,852
Total Loans Receivable	513,576
Commercial and industrial | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	513,576	656,364
Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	676
2018	963
2017	1,439
2016	0
Prior	2,837
Revolving	2,713
Total Loans Receivable	8,628
Commercial and industrial | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	8,628	12,101
Commercial and industrial | Accruing Classified
Financing Receivable, Credit Quality Indicator [Line Items]
2020	200
2019	4,423
2018	7,455
2017	14,726
2016	1,358
Prior	442
Revolving	11,291
Total Loans Receivable	39,895
Commercial and industrial | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	3,649	582
Commercial and industrial | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	39,895	24,987
Paycheck Protection Program
Financing Receivable, Credit Quality Indicator [Line Items]
2020	370,034
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Total Loans Receivable	370,034	0
Paycheck Protection Program | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	370,034
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Total Loans Receivable	370,034
Paycheck Protection Program | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	370,034
Paycheck Protection Program | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	0
Paycheck Protection Program | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	0
Paycheck Protection Program | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	0
Commercial tax-exempt
Financing Receivable, Credit Quality Indicator [Line Items]
2020	12,665
2019	15,912
2018	40,819
2017	28,581
2016	107,595
Prior	213,692
Revolving	0
Total Loans Receivable	419,264	447,927
Commercial tax-exempt | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	12,665
2019	15,912
2018	40,819
2017	24,606
2016	107,595
Prior	206,729
Revolving	0
Total Loans Receivable	408,326
Commercial tax-exempt | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	408,326	436,721
Commercial tax-exempt | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	2,460
Revolving	0
Total Loans Receivable	2,460
Commercial tax-exempt | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	2,460	7,154
Commercial tax-exempt | Accruing Classified
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	3,975
2016	0
Prior	4,503
Revolving	0
Total Loans Receivable	8,478
Commercial tax-exempt | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	0	0
Commercial tax-exempt | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	8,478	4,052
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	209,250
2019	532,982
2018	287,596
2017	340,806
2016	440,361
Prior	792,302
Revolving	73,411
Total Loans Receivable	2,676,708	2,551,274
Commercial real estate | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	5,285
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Total Loans Receivable	5,285
Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	187,358
2019	481,495
2018	260,482
2017	338,837
2016	393,779
Prior	725,465
Revolving	73,411
Total Loans Receivable	2,460,827
Commercial real estate | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	2,460,827	2,495,702
Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	20,640
2019	34,666
2018	27,114
2017	790
2016	37,704
Prior	54,747
Revolving	0
Total Loans Receivable	175,661
Commercial real estate | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	175,661	32,014
Commercial real estate | Accruing Classified
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,252
2019	11,536
2018	0
2017	1,179
2016	8,878
Prior	12,090
Revolving	0
Total Loans Receivable	34,935
Commercial real estate | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	5,285	0
Commercial real estate | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	34,935	23,558
Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
2020	5,937
2019	61,095
2018	82,528
2017	47,276
2016	16,928
Prior	26,447
Revolving	0
Total Loans Receivable	240,211	225,983
Construction and land | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	5,937
2019	61,095
2018	77,695
2017	47,276
2016	16,928
Prior	26,447
Revolving	0
Total Loans Receivable	235,378
Construction and land | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	235,378	225,526
Construction and land | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	4,833
2017	0
2016	0
Prior	0
Revolving	0
Total Loans Receivable	4,833
Construction and land | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	4,833	457
Construction and land | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	0	0
Construction and land | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	0	0
Residential
Financing Receivable, Credit Quality Indicator [Line Items]
2020	332,172
2019	583,691
2018	449,714
2017	461,756
2016	438,329
Prior	593,965
Revolving	0
Total Loans Receivable	2,859,627	2,839,155
Residential | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	262
2018	1,084
2017	2,529
2016	0
Prior	12,519
Revolving	0
Total Loans Receivable	16,394
Residential | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	332,172
2019	583,429
2018	448,630
2017	459,227
2016	438,329
Prior	577,218
Revolving	0
Total Loans Receivable	2,839,005
Residential | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	2,839,005	2,820,909
Residential | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	0	0
Residential | Accruing Classified
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	4,228
Revolving	0
Total Loans Receivable	4,228
Residential | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	16,394	13,993
Residential | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	4,228	4,253
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	454
2017	248
2016	686
Prior	14,104
Revolving	69,096
Total Loans Receivable	84,588	83,657
Home equity | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	56
Revolving	139
Total Loans Receivable	195
Home equity | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	454
2017	248
2016	686
Prior	12,998
Revolving	68,957
Total Loans Receivable	83,343
Home equity | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	83,343	81,060
Home equity | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	0	0
Home equity | Accruing Classified
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	1,050
Revolving	0
Total Loans Receivable	1,050
Home equity | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	195	1,525
Home equity | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	1,050	1,072
Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,388
2019	318
2018	111
2017	0
2016	88
Prior	806
Revolving	114,063
Total Loans Receivable	116,774	134,674
Consumer and other | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	73
2017	0
2016	0
Prior	0
Revolving	8
Total Loans Receivable	81
Consumer and other | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	300
Total Loans Receivable	300
Consumer and other | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,388
2019	318
2018	38
2017	0
2016	88
Prior	806
Revolving	113,755
Total Loans Receivable	116,393
Consumer and other | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	116,393	134,371
Consumer and other | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	300	300
Consumer and other | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	81	3
Consumer and other | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	$ 0	$ 0