Income Taxes - Summary of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Expected federal tax expense	$ 9,126	$ 8,158	$ 7,371
Tax impact from enacted change in tax rate	2,747	0	0
Nondeductible interest expense	85	94	78
Tax-exempt interest	(949)	(1,265)	(1,338)
State income taxes	296	296	222
Other, net	(479)	(276)	(313)
Total income tax expense	10,826	7,007	6,020
Downward adjustment of net deferred tax assets	$ 2,747	$ 0	$ 0