Deposit Accounts - Interest expense on deposit accounts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest expense on deposit accounts
Checking accounts	$ 200,000	$ 165,000	$ 161,000
Money market accounts	3,641,000	2,426,000	1,443,000
Savings	151,000	141,000	110,000
Certificates of deposit accounts	4,399,000	3,898,000	3,323,000
Total	8,391,000	6,630,000	$ 5,037,000
Accrued interest on deposits	$ 178,000	$ 124,000