Other Real Estate - Company's Other Real Estate (Detail) $ in Thousands	Dec. 31, 2017 USD ($) Property	Dec. 31, 2016 USD ($) Property	Dec. 31, 2015 USD ($) Property
Real Estate By Property [Line Items]
Number of Properties | Property	19	25	26
Balance | $	$ 8,232	$ 8,513	$ 9,916
Construction, Land Development and Other Land [Member]
Real Estate By Property [Line Items]
Number of Properties | Property	14	19	19
Balance | $	$ 6,670	$ 7,658	$ 8,792
1 - 4 Family Residential Properties [Member]
Real Estate By Property [Line Items]
Number of Properties | Property	5	3	3
Balance | $	$ 1,562	$ 202	$ 368
Nonfarm Nonresidential [Member]
Real Estate By Property [Line Items]
Number of Properties | Property		3	4
Balance | $		$ 653	$ 756