Securities Sold Under Agreements to Repurchase - Summary of Balances for Securities Sold Under Agreements to Repurchase (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Assets Sold Under Agreements To Repurchase [Line Items]
Balance at year end	$ 14,293	$ 21,561
Mortgage Backed Securities
Assets Sold Under Agreements To Repurchase [Line Items]
Balance at year end	14,293	21,561
Average daily balance during the year	$ 16,326	$ 60,331
Average interest rate during the year	0.17%	0.11%
Maximum month-end balance during the year	$ 19,432	$ 115,005
Weighted average interest rate at year-end	0.16%	0.17%