Borrowings - Long-term debt (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Long-term debt
Long-term debt	$ 50,000	$ 50,000
FHLB advances
Long-term debt
Long-term debt	$ 50,000	$ 50,000
Weighted average rate (as a percent)	1.71%	1.19%
FHLB advances | Minimum
Long-term debt
Interest rate (as a percent)	1.60%	1.10%
FHLB advances | Maximum
Long-term debt
Interest rate (as a percent)	1.87%	1.32%