Income Taxes - Reconciliation of Tax Expense at the Federal Statutory Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Tax expense at the federal statutory tax rate	$ 25,937	$ 35,377	$ 33,546
Increase (decrease) in tax expense from:
Tax-exempt income, net	(507)	(581)	(510)
Modified endowment life contracts	(508)	(519)	(558)
Share based compensation excess tax benefit	(412)	(765)	(917)
Tax deductible dividends paid on ESOP	(453)
State tax expense, net of federal tax benefit	5,606	5,757	5,595
Utilization of tax credits:
New markets tax credits, net of tax expense	(3,121)	(3,547)	(1,422)
Low-income housing tax credits, net of amortization	(1,273)	(1,266)	(1,273)
Other tax credits	(320)
Other, net	(1,023)	227	(523)
Total income taxes	$ 23,926	$ 34,683	$ 33,938