Fair Value Measurements - Fair Value Measurement on Nonrecurring Basis (Details) - Nonrecurring - Impaired Loans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Basis	$ 1,504	$ 976
Fair Value	1,216	307
Net Losses (Gains) Recorded in Earnings	168	(558)
Level 1
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Level 2
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	1,216	307
One-to-four family residential
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Basis		976
Fair Value		307
Net Losses (Gains) Recorded in Earnings		(558)
One-to-four family residential | Level 1
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value		0
One-to-four family residential | Level 2
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value		0
One-to-four family residential | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value		$ 307
Commercial business
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Basis	1,495
Fair Value	1,209
Net Losses (Gains) Recorded in Earnings	160
Commercial business | Level 1
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0
Commercial business | Level 2
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0
Commercial business | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	1,209
Commercial business | Commercial and industrial
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Basis	117
Fair Value	107
Net Losses (Gains) Recorded in Earnings	10
Commercial business | Commercial and industrial | Level 1
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0
Commercial business | Commercial and industrial | Level 2
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0
Commercial business | Commercial and industrial | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	107
Commercial business | Non-owner occupied commercial real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Basis	1,378
Fair Value	1,102
Net Losses (Gains) Recorded in Earnings	150
Commercial business | Non-owner occupied commercial real estate | Level 1
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0
Commercial business | Non-owner occupied commercial real estate | Level 2
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0
Commercial business | Non-owner occupied commercial real estate | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	1,102
Consumer
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Basis	9
Fair Value	7
Net Losses (Gains) Recorded in Earnings	8
Consumer | Level 1
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0
Consumer | Level 2
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0
Consumer | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	$ 7