Goodwill and Other Intangible Assets - Gross Carrying Value and Accumulated Amortization of Other Intangible Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 461,000	$ 461,000
Accumulated Amortization	135,936	126,699
Net Carrying Amount	325,064	334,301
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	328,837	328,837
Accumulated Amortization	82,210	76,795
Net Carrying Amount	246,627	252,042
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	122,063	122,063
Accumulated Amortization	50,503	47,186
Net Carrying Amount	71,560	74,877
Non-competition agreement
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,000	4,000
Accumulated Amortization	1,800	1,600
Net Carrying Amount	2,200	2,400
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,100	6,100
Accumulated Amortization	1,423	1,118
Net Carrying Amount	$ 4,677	$ 4,982