Loan Portfolio and Credit Quality Loans by Grade or Nonaccrual Status (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 241,050
2019	1,405,232
2018	1,124,350
2017	1,065,025
2016	1,112,476
2015 & Prior	2,095,205
Total Loans Receivable	7,043,338	$ 6,976,704
Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	5,826
2018	1,089
2017	2,742
2016	874
2015 & Prior	13,783
Total Loans Receivable	24,314
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	241,000
2019	1,349,414
2018	1,104,102
2017	1,022,649
2016	1,080,606
2015 & Prior	2,040,682
Total Loans Receivable	6,838,453
Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	6,838,453	6,850,653
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	23,343
2018	15,557
2017	19,460
2016	19,557
2015 & Prior	14,706
Total Loans Receivable	92,623
Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	92,623	52,026
Accruing Classified
Financing Receivable, Credit Quality Indicator [Line Items]
2020	50
2019	26,649
2018	3,602
2017	20,174
2016	11,439
2015 & Prior	26,034
Total Loans Receivable	87,948
Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	24,314	16,103
Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	87,948	57,922
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	27,037
2019	175,877
2018	152,717
2017	70,767
2016	43,312
2015 & Prior	201,034
Total Loans Receivable	670,744	694,034
Commercial and industrial | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	171
2018	0
2017	210
2016	735
2015 & Prior	255
Total Loans Receivable	1,371
Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	26,987
2019	149,993
2018	147,350
2017	51,752
2016	39,825
2015 & Prior	193,630
Total Loans Receivable	609,537
Commercial and industrial | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	609,537	656,364
Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	488
2018	1,765
2017	3,836
2016	232
2015 & Prior	3,107
Total Loans Receivable	9,428
Commercial and industrial | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	9,428	12,101
Commercial and industrial | Accruing Classified
Financing Receivable, Credit Quality Indicator [Line Items]
2020	50
2019	25,225
2018	3,602
2017	14,969
2016	2,520
2015 & Prior	4,042
Total Loans Receivable	50,408
Commercial and industrial | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	1,371	582
Commercial and industrial | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	50,408	24,987
Commercial tax-exempt
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	13,741
2018	41,012
2017	28,844
2016	108,057
2015 & Prior	253,665
Total Loans Receivable	445,319	447,927
Commercial tax-exempt | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	13,741
2018	41,012
2017	24,823
2016	108,057
2015 & Prior	246,626
Total Loans Receivable	434,259
Commercial tax-exempt | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	434,259	436,721
Commercial tax-exempt | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 & Prior	2,516
Total Loans Receivable	2,516
Commercial tax-exempt | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	2,516	7,154
Commercial tax-exempt | Accruing Classified
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	4,021
2016	0
2015 & Prior	4,523
Total Loans Receivable	8,544
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	8,544	4,052
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	71,236
2019	521,625
2018	324,001
2017	365,669
2016	460,893
2015 & Prior	882,875
Total Loans Receivable	2,626,299	2,551,274
Commercial real estate | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	5,392
2018	0
2017	0
2016	0
2015 & Prior	0
Total Loans Receivable	5,392
Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	71,236
2019	491,954
2018	310,679
2017	349,161
2016	432,649
2015 & Prior	861,627
Total Loans Receivable	2,517,306
Commercial real estate | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	2,517,306	2,495,702
Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	22,855
2018	13,322
2017	15,324
2016	19,325
2015 & Prior	9,083
Total Loans Receivable	79,909
Commercial real estate | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	79,909	32,014
Commercial real estate | Accruing Classified
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	1,424
2018	0
2017	1,184
2016	8,919
2015 & Prior	12,165
Total Loans Receivable	23,692
Commercial real estate | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	5,392	0
Commercial real estate | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	23,692	23,558
Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,731
2019	52,620
2018	85,162
2017	53,428
2016	16,820
2015 & Prior	26,532
Total Loans Receivable	238,293	225,983
Construction and land | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,731
2019	52,620
2018	84,692
2017	53,428
2016	16,820
2015 & Prior	26,532
Total Loans Receivable	237,823
Construction and land | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	237,823	225,526
Construction and land | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	470
2017	0
2016	0
2015 & Prior	0
Total Loans Receivable	470
Construction and land | Special Mention | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	470	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	131,395
2019	612,363
2018	481,618
2017	507,204
2016	471,195
2015 & Prior	638,151
Total Loans Receivable	2,841,926	2,839,155
Residential | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	263
2018	1,089
2017	2,532
2016	0
2015 & Prior	12,190
Total Loans Receivable	16,074
Residential | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	131,395
2019	612,100
2018	480,529
2017	504,672
2016	471,195
2015 & Prior	621,720
Total Loans Receivable	2,821,611
Residential | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	2,821,611	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
2015 & Prior	4,241
Total Loans Receivable	4,241
Residential | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	16,074	13,993
Residential | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	4,241	4,253
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,325
2019	13,322
2018	15,847
2017	7,781
2016	6,972
2015 & Prior	44,103
Total Loans Receivable	89,350	83,657
Home equity | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	139
2015 & Prior	1,337
Total Loans Receivable	1,476
Home equity | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,325
2019	13,322
2018	15,847
2017	7,781
2016	6,833
2015 & Prior	41,703
Total Loans Receivable	86,811
Home equity | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	86,811	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
2015 & Prior	1,063
Total Loans Receivable	1,063
Home equity | Accruing Classified | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	1,476	1,525
Home equity | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	1,063	1,072
Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	6,326
2019	15,684
2018	23,993
2017	31,332
2016	5,227
2015 & Prior	48,845
Total Loans Receivable	131,407	134,674
Consumer and other | Nonaccrual Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015 & Prior	1
Total Loans Receivable	1
Consumer and other | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	300
2016	0
2015 & Prior	0
Total Loans Receivable	300
Consumer and other | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	6,326
2019	15,684
2018	23,993
2017	31,032
2016	5,227
2015 & Prior	48,844
Total Loans Receivable	131,106
Consumer and other | Pass | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	131,106	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	1	3
Consumer and other | Accruing Classified | Performing Financial Instruments
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans Receivable	$ 0	$ 0