Consolidated Statements of Shareholders' Equity (Parenthetical) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares
Statement of Stockholders' Equity [Abstract]
Tax effect on employee benefit funded status adjustment | $	$ 292	$ (1,019)	$ (122)
Cash dividends (in dollars per share)	$ 0.49	$ 0.43	$ 0.39
Issuance of treasury stock (in shares) | shares	61	41	70
Common stock, par value (in dollars per share)	$ 1	$ 1