Income Taxes - Summary of Reconciliation of Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Computed “expected” tax expense									$ 3,152	$ 8,491	$ 16,321
State tax expense, net of federal tax effect									(1,924)	(612)	333
Effective of statutory rate changes enacted									0	0	5,323
Non-deductible merger costs									0	67	19
Incentive stock options									439	475	506
Bank owned life insurance									(310)	(320)	(286)
Tax-exempt interest income, net of expense									(875)	(1,296)	(2,585)
Insurance premiums									(324)	(293)	(347)
Excess tax benefit from exercise of stock options and vesting of restricted stock									(201)	(647)	(805)
Other									230	47	52
Income tax expense	$ (2,970)	$ 2,117	$ 706	$ 334	$ 122	$ 1,068	$ 2,263	$ 2,459	$ 187	$ 5,912	$ 18,531