CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other comprehensive income (loss):
Net unrealized gain (loss) on available-for-sale securities, tax expense (benefit)	$ 285	$ (1,242)	$ (169)
Net realized gain on sale of available-for-sale securities included in net income, tax expense (benefit)	81	370	168
Change in nonqualified pension plan unrecognized net gain (loss) and unrecognized prior service cost, tax expense (benefit)	$ (53)	$ 128	$ 55