Loans and Allowance for Credit Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Past Due [Line Items]
Total	$ 7,656,034	$ 7,653,341
Nonaccrual	33,209	22,947	$ 19,052
Current
Financing Receivable, Past Due [Line Items]
Total	7,599,427	7,615,273
Total Past Due Loans
Financing Receivable, Past Due [Line Items]
Total	56,607	38,068
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	14,019	7,247
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	9,379	7,874
Commercial Loans | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total	2,699,782	2,659,135
Nonaccrual	17,153	6,320	7,100
Commercial Loans | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	1,410,517	1,436,183
Nonaccrual	612	878	283
Commercial Loans | Commercial construction
Financing Receivable, Past Due [Line Items]
Total	347,375	350,583
Nonaccrual	4,960	4,960	384
Commercial Loans | Business banking
Financing Receivable, Past Due [Line Items]
Total	1,307,155	1,360,765
Nonaccrual	3,907	4,147	4,490
Commercial Loans | Current | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total	2,682,629	2,649,412
Commercial Loans | Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	1,399,799	1,435,301
Commercial Loans | Current | Commercial construction
Financing Receivable, Past Due [Line Items]
Total	342,415	345,623
Commercial Loans | Current | Business banking
Financing Receivable, Past Due [Line Items]
Total	1,297,451	1,351,048
Commercial Loans | Total Past Due Loans | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total	17,153	9,723
Commercial Loans | Total Past Due Loans | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	10,718	882
Commercial Loans | Total Past Due Loans | Commercial construction
Financing Receivable, Past Due [Line Items]
Total	4,960	4,960
Commercial Loans | Total Past Due Loans | Business banking
Financing Receivable, Past Due [Line Items]
Total	9,704	9,717
Commercial Loans | 30-59 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total	0	0
Commercial Loans | 30-59 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	2,109	4
Commercial Loans | 30-59 Days Past Due | Commercial construction
Financing Receivable, Past Due [Line Items]
Total	0	0
Commercial Loans | 30-59 Days Past Due | Business banking
Financing Receivable, Past Due [Line Items]
Total	5,487	3,525
Commercial Loans | 60-89 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total	0	3,403
Commercial Loans | 60-89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	7,997	0
Commercial Loans | 60-89 Days Past Due | Commercial construction
Financing Receivable, Past Due [Line Items]
Total	0	0
Commercial Loans | 60-89 Days Past Due | Business banking
Financing Receivable, Past Due [Line Items]
Total	310	2,045
Consumer Loans | Consumer real estate
Financing Receivable, Past Due [Line Items]
Total	1,782,973	1,731,778
Nonaccrual	6,371	6,312	6,526
Consumer Loans | Other consumer
Financing Receivable, Past Due [Line Items]
Total	108,232	114,897
Nonaccrual	206	330	$ 269
Consumer Loans | Current | Consumer real estate
Financing Receivable, Past Due [Line Items]
Total	1,769,518	1,719,751
Consumer Loans | Current | Other consumer
Financing Receivable, Past Due [Line Items]
Total	107,615	114,138
Consumer Loans | Total Past Due Loans | Consumer real estate
Financing Receivable, Past Due [Line Items]
Total	13,455	12,027
Consumer Loans | Total Past Due Loans | Other consumer
Financing Receivable, Past Due [Line Items]
Total	617	759
Consumer Loans | 30-59 Days Past Due | Consumer real estate
Financing Receivable, Past Due [Line Items]
Total	6,204	3,352
Consumer Loans | 30-59 Days Past Due | Other consumer
Financing Receivable, Past Due [Line Items]
Total	219	366
Consumer Loans | 60-89 Days Past Due | Consumer real estate
Financing Receivable, Past Due [Line Items]
Total	880	2,363
Consumer Loans | 60-89 Days Past Due | Other consumer
Financing Receivable, Past Due [Line Items]
Total	$ 192	$ 63