Income Taxes - Summary of Differences in Taxes from Continuing Operations Computed at Statutory Rate (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Provision at statutory rate of 35%	$ 16,269	$ 12,827
Tax-exempt income	(4,397)	(4,168)
State income taxes	851	583
Interim period effective rate adjustment	(455)	(148)
Tax credit investments	(1,876)	(80)
Other, net	99	657
Income tax expense	$ 10,491	$ 9,671
Effective tax rate	22.60%	26.40%