Loans and Allowance for Loan Losses - Summary of Loans Modified as Troubled Debt Restructurings for Payment Default (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Troubled Debt Restructurings [Line Items]
Defaulted	$ 0	$ 0
Charge offs and specific reserves	76,000		$ 132,000
Residential Real Estate
Troubled Debt Restructurings [Line Items]
Defaulted			145,000
Charge offs and specific reserves			45,000
Residential Real Estate | 1-to-4 Family Mortgage
Troubled Debt Restructurings [Line Items]
Defaulted			145,000
Charge offs and specific reserves	$ 8,000		$ 45,000