Deposit Accounts - Interest expense on deposit accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest expense on deposit accounts
Checking accounts	$ 365	$ 200	$ 165
Money market accounts	6,720	3,641	2,426
Savings	251	151	141
Certificates of deposit accounts	6,035	4,399	3,898
Total	13,371	8,391	$ 6,630
Accrued interest on deposits	$ 526	$ 178