Revenue from Contracts with Customers - Schedule of Revenue from Contracts (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
Disaggregation of Revenue [Line Items]
Total net interest income	$ 25,331	$ 23,770	$ 23,250	$ 23,438	$ 23,705	$ 23,204	$ 23,199	$ 22,468	$ 95,789	$ 92,576	$ 85,616
Noninterest income:
Service charges on deposit accounts									9,220	8,560	8,586
Lockbox fees									3,973	3,274	3,290
Brokerage commissions									277	348	353
Net gains on sales of securities									61	302	47
Gains on sales of mortgage loans									412		370
Other income									4,456	3,764	3,906
Total other operating income	$ 4,689	$ 4,286	$ 4,997	$ 4,427	$ 4,164	$ 4,169	$ 3,722	$ 4,193	18,399	16,248	16,552
ASU 2014-09 [Member]
Disaggregation of Revenue [Line Items]
Total net interest income									95,789	92,576	85,616
Noninterest income:
Service charges on deposit accounts									9,220	8,560	8,586
Lockbox fees									3,973	3,274	3,290
Brokerage commissions									277	348	353
Net gains on sales of securities									61	302	47
Gains on sales of mortgage loans									412		370
Other income									4,456	3,764	3,906
Total other operating income									18,399	16,248	16,552
Total revenues									114,188	108,824	102,168
ASU 2014-09 [Member] | Revenue Guidance Contracts in Scope of Topic 606 [Member]
Noninterest income:
Service charges on deposit accounts									9,220	8,560	8,586
Lockbox fees									3,973	3,274	3,290
Other income									2,799	2,536	2,429
Total other operating income									15,992	14,370	14,305
Total revenues									$ 15,992	$ 14,370	$ 14,305