Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended	12 Months Ended
	Jan. 01, 2018	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Federal Statutory Income Tax Rate			21.00%	35.00%
Unrealized gain or loss on available-for-sale equity securities	$ 11
Tax Cuts and Jobs Act of 2017, Re-measured net deferred tax assets		$ 1,086	$ 1,086
Tax Cuts and Jobs Act of 2017, Re-measured net deferred tax assets relating to unrealized losses on securities		535	535
Tax Cuts and Jobs Act of 2017, Stranded Tax Effect			535
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings			535
Other [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Recovery on zero-basis purchased loans, income from equity method investments		36	95
Accounting Standards Update 2014-09 [Member] | Other [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Investment referral income, insurance sales commissions and other non-interest income related to loans and deposits		$ 487	$ 889