Income Taxes - Summary of Differences in Taxes from Continuing Operations Computed at Statutory Rate (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Statutory rate	21.00%
Provision at statutory rate	$ 12,908	$ 16,238	$ 18,279	$ 30,808
Tax-exempt interest	(2,671)	(2,604)	(5,303)	(5,135)
Section 291/265 interest disallowance	44	123	116	234
Company-owned life insurance income	(623)	(569)	(1,270)	(1,239)
Tax-exempt income	(3,250)	(3,050)	(6,457)	(6,140)
State income taxes	1,718	1,558	1,711	3,558
Interim period effective rate adjustment	75	353	3,341	1,041
Tax credit investments - federal	(1,819)	(715)	(3,720)	(1,134)
Other, net	129	(25)	(454)	(670)
Income tax expense	$ 9,761	$ 14,359	$ 12,700	$ 27,463
Effective tax rate	15.90%	18.60%	14.60%	18.70%

Effective Income Tax Rate Reconciliation, Tax Exempt Income, Life Insurance, Amount

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