Income Taxes - Summary of Differences in Taxes from Continuing Operations Computed at Statutory Rate (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Provision at statutory rate	$ 17,437	$ 11,901	$ 48,245	$ 33,171
Tax-exempt interest	(2,511)	(2,179)	(7,645)	(6,607)
Section 291/265 interest disallowance	113	84	346	220
Company-owned life insurance income	(568)	(621)	(1,806)	(1,679)
Tax-exempt income	(2,966)	(2,716)	(9,105)	(8,066)
State income taxes	1,496	2,091	5,053	4,307
Interim period effective rate adjustment	(1,598)	(81)	(557)	944
Tax credit investments - federal	(2,443)	(5,483)	(3,577)	(16,224)
Other, net	1,328	(387)	658	495
Income tax expense	$ 13,254	$ 5,325	$ 40,717	$ 14,627
Effective tax rate	16.00%	9.40%	17.70%	9.30%

Income tax reconciliation, non-deductible expense, interest disallowance.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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