Consolidated Statements of Shareholders' Equity (Parenthetical) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Statement Of Stockholders Equity [Abstract]
Tax effect on employee benefit funded status adjustment | $	$ 5,127	$ 292	$ 1,019
Cash dividends (in dollars per share)	$ 0.56	$ 0.49	$ 0.43
Issuance of treasury stock (in shares) | shares	40	61	41
Common stock, par value (in dollars per share)	$ 1	$ 1	$ 1