Investment Securities - Gross unrealized losses and fair value, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position (Parentheticals) (Details 2) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Mortgage-backed securities - residential
Available For Sale And Held To Maturity Securities Unrealized Loss Position [Line Items]
Aggregate unrealized loss position	$ 500	$ 500