Deposit Accounts - Interest expense on deposit accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest expense on deposit accounts
Checking accounts	$ 1,167	$ 365	$ 200
Money market accounts	19,567	6,720	3,641
Savings	357	251	151
Certificates of deposit accounts	16,562	6,035	4,399
Total	37,653	13,371	$ 8,391
Accrued interest on deposits	$ 1,742	$ 526