Income Taxes - Reconciliation of Tax Expense at the Federal Statutory Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax expense at the federal statutory tax rate	$ 35,377	$ 33,546	$ 47,708
Increase (decrease) in tax expense from:
Tax-exempt income, net	(581)	(510)	(829)
Modified endowment life contracts	(519)	(558)	(921)
Share based compensation excess tax benefit	(765)	(917)	(2,354)
State tax expense, net of federal tax benefit	5,757	5,595	3,840
Write-down of net deferred tax asset			4,331
Utilization of tax credits:
New markets tax credits, net of tax expense	(3,547)	(1,422)	(1,151)
Low-income housing tax credits, net of amortization	(1,266)	(1,273)	(1,589)
Other, net	227	(523)	831
Total income taxes	$ 34,683	$ 33,938	$ 49,866