Basis of Presentation and Consolidation - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retained earnings
Subsidiary or Equity Method Investee [Line Items]
Cumulative effect on change in accounting principle			$ (27,000)
ASU 2018-02 | Retained earnings
Subsidiary or Equity Method Investee [Line Items]
Cumulative effect on change in accounting principle		$ 279,000
ASU 2016-01 | Retained earnings
Subsidiary or Equity Method Investee [Line Items]
Cumulative effect on change in accounting principle		$ 173,000
1-4 Family Residential
Subsidiary or Equity Method Investee [Line Items]
Origination covenants, maximum loan-to-value ratio (greater than) (percent)	80.00%