Securities Sold Under Agreements to Repurchase - Contractual Maturity of the Agreements (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	$ 99,600	$ 122,000
U.S. Government agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	99,551	122,019
U.S. Government agencies | Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	99,551	122,019
U.S. Government agencies | Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	0	0
U.S. Government agencies | 30-90 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	0	0
U.S. Government agencies | Greater than 90 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	$ 0	$ 0