Deposits - Maturities of deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deposits
Due within one year	$ 407,149
Due in one year to two years	954
Due in two years to three years	90
Due in three years to four years	749
Due in four years to five years	14
Total time deposits	408,956	$ 166,243
Certificates of deposit of 250,000 or more	$ 56,800	$ 27,800