Loans and Allowance for Credit Losses - Loan Balances by Year of Origination and Internally Assigned Risk Rating (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Total Loan Balance
Current fiscal year	$ 135,359		$ 1,117,436
Year two	1,138,128		1,320,936
Year three	1,309,559		1,094,225
Year four	1,059,734		503,703
Year five	485,560		645,502
More than five years	2,210,198		1,650,211
Revolving	1,287,473		1,292,135
Revolving-Term	30,023		29,193
Total	7,656,034		7,653,341
Year-to-date Gross Charge-offs
Current fiscal year	191		830
Year two	9		214
Year three	27		218
Year four	575		25
Year five	17		3,989
More than five years	5,417		18,669
Revolving	500		109
Revolving-Term	203		584
Total	6,939	$ 4,459	24,638
Pass
Total Loan Balance
Current fiscal year	135,359		1,117,247
Year two	1,135,064		1,318,412
Year three	1,306,243		1,060,514
Year four	1,026,435		499,034
Year five	480,960		595,848
More than five years	2,000,409		1,473,853
Revolving	1,244,443		1,253,528
Revolving-Term	26,766		25,838
Total	7,355,679		7,344,274
Special mention
Total Loan Balance
Current fiscal year	0		189
Year two	3,064		1,681
Year three	2,432		16,493
Year four	17,177		224
Year five	222		24,920
More than five years	108,753		87,973
Revolving	15,529		4,163
Revolving-Term	165		172
Total	147,342		135,815
Substandard
Total Loan Balance
Current fiscal year	0		0
Year two	0		843
Year three	884		17,218
Year four	16,122		4,445
Year five	4,378		24,734
More than five years	101,036		88,385
Revolving	27,501		34,444
Revolving-Term	3,092		3,183
Total	153,013		173,252
Doubtful
Total Loan Balance
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 Loans | Commercial real estate
Total Loan Balance
Current fiscal year	25,970		276,677
Year two	281,115		324,469
Year three	351,226		439,308
Year four	464,794		240,256
Year five	228,899		419,371
More than five years	1,313,640		926,636
Revolving	34,138		32,418
Revolving-Term	0		0
Total	2,699,782		2,659,135
Year-to-date Gross Charge-offs
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	5,205		1,706
Revolving	0		0
Revolving-Term	0		0
Total	5,205	0	1,706
Commercial Loans | Commercial and industrial
Total Loan Balance
Current fiscal year	13,824		171,861
Year two	174,698		231,978
Year three	227,563		210,636
Year four	188,869		54,696
Year five	52,253		52,858
More than five years	228,371		193,905
Revolving	524,939		520,249
Revolving-Term	0		0
Total	1,410,517		1,436,183
Year-to-date Gross Charge-offs
Current fiscal year	0		0
Year two	0		0
Year three	0		0
Year four	537		0
Year five	0		3,412
More than five years	91		15,842
Revolving	500		0
Revolving-Term	0		0
Total	1,128	3,412	19,254
Commercial Loans | Commercial construction
Total Loan Balance
Current fiscal year	13,086		75,596
Year two	90,954		154,456
Year three	141,982		82,313
Year four	65,353		14,845
Year five	14,758		4,727
More than five years	9,008		4,438
Revolving	12,234		14,208
Revolving-Term	0		0
Total	347,375		350,583
Year-to-date Gross Charge-offs
Current fiscal year	0		0
Year two	0		0
Year three	0		0
Year four	0		0
Year five	0		451
More than five years	0		0
Revolving	0		0
Revolving-Term	0		0
Total	0	0	451
Commercial Loans | Business banking
Total Loan Balance
Current fiscal year	32,910		270,129
Year two	254,296		262,606
Year three	241,359		207,611
Year four	190,039		88,018
Year five	85,071		99,574
More than five years	407,132		334,766
Revolving	95,068		96,754
Revolving-Term	1,280		1,307
Total	1,307,155		1,360,765
Year-to-date Gross Charge-offs
Current fiscal year	0		0
Year two	0		67
Year three	0		43
Year four	0		1
Year five	0		88
More than five years	98		1,073
Revolving	0		34
Revolving-Term	0		0
Total	98	652	1,306
Commercial Loans | Pass | Commercial real estate
Total Loan Balance
Current fiscal year	25,970		276,677
Year two	281,115		323,463
Year three	349,797		433,308
Year four	458,810		237,901
Year five	226,569		383,799
More than five years	1,144,226		781,465
Revolving	34,138		32,418
Revolving-Term	0		0
Total	2,520,625		2,469,031
Commercial Loans | Pass | Commercial and industrial
Total Loan Balance
Current fiscal year	13,824		171,672
Year two	173,323		231,114
Year three	226,390		185,884
Year four	165,616		53,101
Year five	50,753		47,063
More than five years	212,441		183,165
Revolving	482,770		482,490
Revolving-Term	0		0
Total	1,325,117		1,354,489
Commercial Loans | Pass | Commercial construction
Total Loan Balance
Current fiscal year	13,086		75,596
Year two	90,954		154,456
Year three	141,982		82,313
Year four	65,353		14,845
Year five	14,758		151
More than five years	4,048		4,054
Revolving	12,234		14,208
Revolving-Term	0		0
Total	342,415		345,623
Commercial Loans | Pass | Business banking
Total Loan Balance
Current fiscal year	32,910		270,129
Year two	252,607		262,535
Year three	241,227		204,874
Year four	186,203		87,346
Year five	84,354		96,371
More than five years	392,973		321,360
Revolving	94,920		96,618
Revolving-Term	508		523
Total	1,285,702		1,339,756
Commercial Loans | Special mention | Commercial real estate
Total Loan Balance
Current fiscal year	0		0
Year two	0		1,006
Year three	1,429		6,000
Year four	5,984		0
Year five	0		24,887
More than five years	95,502		75,428
Revolving	0		0
Revolving-Term	0		0
Total	102,915		107,321
Commercial Loans | Special mention | Commercial and industrial
Total Loan Balance
Current fiscal year	0		189
Year two	1,375		620
Year three	949		10,242
Year four	9,849		0
Year five	0		0
More than five years	9,831		8,848
Revolving	15,485		4,126
Revolving-Term	0		0
Total	37,489		24,025
Commercial Loans | Special mention | Commercial construction
Total Loan Balance
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 Loans | Special mention | Business banking
Total Loan Balance
Current fiscal year	0		0
Year two	1,689		55
Year three	54		251
Year four	1,344		224
Year five	222		33
More than five years	3,311		3,508
Revolving	44		37
Revolving-Term	165		172
Total	6,829		4,280
Commercial Loans | Substandard | Commercial real estate
Total Loan Balance
Current fiscal year	0		0
Year two	0		0
Year three	0		0
Year four	0		2,355
Year five	2,330		10,685
More than five years	73,912		69,743
Revolving	0		0
Revolving-Term	0		0
Total	76,242		82,783
Commercial Loans | Substandard | Commercial and industrial
Total Loan Balance
Current fiscal year	0		0
Year two	0		244
Year three	224		14,510
Year four	13,404		1,595
Year five	1,500		5,795
More than five years	6,099		1,892
Revolving	26,684		33,633
Revolving-Term	0		0
Total	47,911		57,669
Commercial Loans | Substandard | Commercial construction
Total Loan Balance
Current fiscal year	0		0
Year two	0		0
Year three	0		0
Year four	0		0
Year five	0		4,576
More than five years	4,960		384
Revolving	0		0
Revolving-Term	0		0
Total	4,960		4,960
Commercial Loans | Substandard | Business banking
Total Loan Balance
Current fiscal year	0		0
Year two	0		16
Year three	78		2,486
Year four	2,492		448
Year five	495		3,170
More than five years	10,848		9,898
Revolving	104		99
Revolving-Term	607		612
Total	14,624		16,729
Commercial Loans | Doubtful | Commercial real estate
Total Loan Balance
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 Loans | Doubtful | Commercial and industrial
Total Loan Balance
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 Loans | Doubtful | Commercial construction
Total Loan Balance
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 Loans | Doubtful | Business banking
Total Loan Balance
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 Loans | Consumer real estate
Total Loan Balance
Current fiscal year	46,543		311,887
Year two	327,577		335,462
Year three	336,640		147,850
Year four	145,121		102,041
Year five	101,308		67,890
More than five years	250,783		189,794
Revolving	549,482		552,080
Revolving-Term	25,519		24,774
Total	1,782,973		1,731,778
Year-to-date Gross Charge-offs
Current fiscal year	0		0
Year two	0		1
Year three	0		0
Year four	0		5
Year five	9		1
More than five years	14		43
Revolving	0		75
Revolving-Term	116		296
Total	139	77	421
Consumer Loans | Other consumer
Total Loan Balance
Current fiscal year	3,026		11,286
Year two	9,488		11,965
Year three	10,789		6,507
Year four	5,558		3,847
Year five	3,271		1,082
More than five years	1,264		672
Revolving	71,612		76,426
Revolving-Term	3,224		3,112
Total	108,232		114,897
Year-to-date Gross Charge-offs
Current fiscal year	191		830
Year two	9		146
Year three	27		175
Year four	38		19
Year five	8		37
More than five years	9		5
Revolving	0		0
Revolving-Term	87		288
Total	369	$ 318	1,500
Consumer Loans | Pass | Consumer real estate
Total Loan Balance
Current fiscal year	46,543		311,887
Year two	327,577		334,879
Year three	336,058		147,652
Year four	144,925		101,999
Year five	101,267		67,402
More than five years	245,620		183,283
Revolving	548,769		551,368
Revolving-Term	23,048		22,206
Total	1,773,807		1,720,676
Consumer Loans | Pass | Other consumer
Total Loan Balance
Current fiscal year	3,026		11,286
Year two	9,488		11,965
Year three	10,789		6,483
Year four	5,528		3,842
Year five	3,259		1,062
More than five years	1,101		526
Revolving	71,612		76,426
Revolving-Term	3,210		3,109
Total	108,013		114,699
Consumer Loans | Special mention | Consumer real estate
Total Loan Balance
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	109		189
Revolving	0		0
Revolving-Term	0		0
Total	109		189
Consumer Loans | Special mention | Other consumer
Total Loan Balance
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 Loans | Substandard | Consumer real estate
Total Loan Balance
Current fiscal year	0		0
Year two	0		583
Year three	582		198
Year four	196		42
Year five	41		488
More than five years	5,054		6,322
Revolving	713		712
Revolving-Term	2,471		2,568
Total	9,057		10,913
Consumer Loans | Substandard | Other consumer
Total Loan Balance
Current fiscal year	0		0
Year two	0		0
Year three	0		24
Year four	30		5
Year five	12		20
More than five years	163		146
Revolving	0		0
Revolving-Term	14		3
Total	219		198
Consumer Loans | Doubtful | Consumer real estate
Total Loan Balance
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 Loans | Doubtful | Other consumer
Total Loan Balance
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