Deposits - Certificates of deposits and Scheduled maturities of time deposits - (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Deposits
Aggregate amounts of certificates of deposits in denominations of $250,000 or more	$ 336,900,000	$ 325,300,000	$ 183,100,000
Increased insurance limit on deposit accounts	250,000		250,000
Traditional, out-of-market brokered deposits	$ 19,800,000	$ 43,600,000	$ 42,500,000