Consolidated Statements of Shareholders' Equity (Parenthetical) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Statement Of Stockholders Equity [Abstract]
Tax effect on employee benefit funded status adjustment | $	$ 69	$ 16	$ 5,127
Cash dividends (in dollars per share)	$ 0.70	$ 0.64	$ 0.56
Issuance of treasury stock (in shares) | shares	22	72	40
Common stock, par value (in dollars per share)	$ 1	$ 1	$ 1