Subordinated Notes (Details) $ in Thousands		4 Months Ended	12 Months Ended
		Dec. 31, 2017	Dec. 31, 2015 USD ($) trust	Dec. 31, 2014 USD ($)
Subordinated Notes
Number of trusts sponsored | trust			1
Percentage of ownership interest			100.00%
Subordinated notes
Amount of subordinated notes			$ 58,764	$ 58,764
June 2007 issuance
Subordinated notes
Amount of subordinated notes			$ 41,238
Interest Rate (as a percent)	[1]		7.22%
Maturity date of subordinated notes			Jun. 15, 2037
August 2007 issuance
Subordinated notes
Amount of subordinated notes			$ 17,526
Interest Rate (as a percent)	[2]		7.10%
Maturity date of subordinated notes			Sep. 15, 2037
London Interbank Offered Rate (LIBOR) | Future interest rate | August 2007 issuance
Subordinated notes
Basis Spread on Variable Rate (as a percent)	[2]	1.48%

[1] Fixed rate through life of debt.

[2] Fixed rate through September 15, 2017 then LIBOR +1.48% through remaining life of debt.