Securities - Cost of Restricted Stock (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Total restricted stock	$ 5,221	$ 6,110	[1]
FRB stock
Schedule of Investments [Line Items]
Total restricted stock	3,595	3,587
FHLB stock
Schedule of Investments [Line Items]
Total restricted stock	$ 1,626	$ 2,523

[1] Derived from audited consolidated financial statements.