Statements of Shareholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Common stock	Capital in Excess of Par Value	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning balance at Dec. 31, 2019	$ 555,959	$ 544	$ 59,900	$ 725,795	$ (77,896)	$ (152,384)
Increase (Decrease) in Stockholders' Equity
Net income	11,517			11,517
Other comprehensive income (loss)	5,190				5,190
Comprehensive income (loss)	16,707
Cash dividends declared	(17,740)			(17,740)
Share-based compensation expense	3,994		3,994
Delivery of treasury shares
RSUs and PSAs	(420)		(2,077)			1,657
Employee stock options exercised — net	(75)		(217)			142
Ending balance at Sep. 30, 2020	558,425	544	61,600	719,572	(72,706)	(150,585)
Beginning balance at Jun. 30, 2020	540,999	544	59,982	719,035	(87,977)	(150,585)
Increase (Decrease) in Stockholders' Equity
Net income	6,527			6,527
Other comprehensive income (loss)	15,271				15,271
Comprehensive income (loss)	21,798
Cash dividends declared	(5,990)			(5,990)
Share-based compensation expense	1,618		1,618
Ending balance at Sep. 30, 2020	558,425	544	61,600	719,572	(72,706)	(150,585)
Beginning balance at Dec. 31, 2020	577,932	544	63,261	723,365	(58,653)	(150,585)
Increase (Decrease) in Stockholders' Equity
Net income	17,331			17,331
Other comprehensive income (loss)	(16,872)				(16,872)
Comprehensive income (loss)	459
Cash dividends declared	(18,469)			(18,469)
Share-based compensation expense	4,015		4,015
Delivery of treasury shares
RSUs and PSAs	(633)		(3,002)			2,369
Ending balance at Sep. 30, 2021	563,304	544	64,274	722,227	(75,525)	(148,216)
Beginning balance at Jun. 30, 2021	571,245	544	62,796	720,934	(64,813)	(148,216)
Increase (Decrease) in Stockholders' Equity
Net income	7,527			7,527
Other comprehensive income (loss)	(10,712)				(10,712)
Comprehensive income (loss)	(3,185)
Cash dividends declared	(6,234)			(6,234)
Share-based compensation expense	1,478		1,478
Ending balance at Sep. 30, 2021	$ 563,304	$ 544	$ 64,274	$ 722,227	$ (75,525)	$ (148,216)