Acquisition - Additional Information (Detail) - USD ($)			6 Months Ended
	Jan. 02, 2018	Oct. 12, 2017	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Business Acquisition [Line Items]
Fair value of total loans			$ 266,327,000
Fair value of purchased credit impaired loans			26,408,000	$ 27,534,000	$ 26,685,000
Contractual amounts			35,235,000	36,614,000	34,412,000
Purchased Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Contractual amounts			750,000	$ 1,157,000	$ 3,918,000
FBC Bancshares, Inc. and First Bank, N.A. [Member]
Business Acquisition [Line Items]
Payment for all outstanding shares of acquired entity by shares		1,289,371
Fair value of total loans			266,327,000
Total loans of contractual amounts			271,714,000
FBC Bancshares, Inc. and First Bank, N.A. [Member] | Purchased Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Fair value of purchased credit impaired loans			3,013,000
Contractual amounts			$ 3,806,000
Commercial Bancshares, Inc [Member]
Business Acquisition [Line Items]
Business acquisition, agreement date			Oct. 12, 2017
Payment for all outstanding shares of acquired entity by shares	1,289,371
Business acquisition, special dividend	$ 22,075,000
Increase decrease in business acquisition, special dividend	$ 42,402,000