Securities Sold Under Agreements to Repurchase (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets Sold under Agreements to Repurchase [Line Items]
Carrying amount of securities pledged as collateral	$ 419,383	$ 398,889
Available-for-sale Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Sweep, Interest rate	0.11%
Assets Sold under Agreements to Repurchase, Sweep, Carrying Amount	$ 54,100
Assets Sold under Agreements to Repurchase, Term, Carrying Amounts	$ 25,000
Assets Sold under Agreements to Repurchase, Term, Interest Rate	1.88%
Repurchase Agreements, Sweep [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Carrying amount of securities pledged as collateral	$ 66,500
Repurchase Agreements,Term [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Carrying amount of securities pledged as collateral	$ 28,500