Consolidated Statement of Shareholders' Equity - USD ($)	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning Balance (in shares) at Dec. 31, 2016		28,162,497
Beginning Balance at Dec. 31, 2016	$ 565,787,000	$ 28,162,000	$ 171,162,000	$ 560,200,000	$ (156,393,000)	$ (37,344,000)
Beginning Balance (in shares) at Dec. 31, 2016						1,054,364
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	49,826,000	0	0	49,826,000	0	$ 0
Other comprehensive income	40,579,000	0			40,579,000	0
Dividends (per share of common stock, $0.80)	(22,149,000)	0	0	(22,149,000)	0	0
Changes due to convertible notes transactions	1,797,000	$ 0	1,797,000	0	0	0
Changes due to convertible notes transactions (in shares)		624,044
Changes due to convertible notes transactions		$ 624,000		$ 0	$ 0	$ 0
Adjustments to Equity, Equity Component of Convertible Debt	(1,958,000)
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature			$ (2,582,000)
Purchase of treasury shares (in shares)		0	0	0	0	218,235
Purchase of treasury shares	(11,552,000)	$ 0				$ (11,552,000)
Employee stock plans (in shares)		265,886
Employee stock plans	7,370,000	$ 266,000	$ 9,074,000	$ 0	$ 0
Employee stock plans (in shares)						39,647
Employee stock plans						$ (1,970,000)
Share-based compensation expense (in shares)		89,040
Share-based compensation expense	5,956,000	$ 89,000	5,881,000	0	0
Share-based compensation expense (in shares)						13,729
Share-based compensation expense						$ (14,000)
Ending Balance (in shares) at Dec. 31, 2017		29,141,467
Ending Balance at Dec. 31, 2017	635,656,000	$ 29,141,000	185,332,000	587,877,000	(115,814,000)	$ (50,880,000)
Ending Balance (in shares) at Dec. 31, 2017						1,325,975
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	54,169,000	0	0	54,169,000	0	$ 0
Cumulative Effect on Retained Earnings, Net of Tax	(9,584,000)	0	0	(9,584,000)	0	0
Other comprehensive income	(19,084,000)	0	0	0	(19,084,000)	0
Dividends (per share of common stock, $0.80)	(22,359,000)	$ 0	0	(22,359,000)	0	$ 0
Changes due to convertible notes transactions (in shares)		114,778				0
Changes due to convertible notes transactions		$ 115,000		0	0	$ 0
Adjustments to Equity, Equity Component of Convertible Debt	(8,000)
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature			(123,000)
Purchase of treasury shares (in shares)		0				313,330
Purchase of treasury shares	(19,489,000)	$ 0	0	0	0	$ (19,489,000)
Employee stock plans (in shares)		226,722
Employee stock plans	7,351,000	$ 227,000	8,813,000	0	0
Employee stock plans (in shares)						(25,069)
Employee stock plans						$ (1,689,000)
Share-based compensation expense (in shares)		61,747
Share-based compensation expense	6,505,000	$ 62,000	6,452,000	0	0
Share-based compensation expense (in shares)						8,543
Share-based compensation expense						$ (9,000)
Ending Balance (in shares) at Dec. 31, 2018		29,544,714
Ending Balance at Dec. 31, 2018	$ 633,157,000	$ 29,545,000	200,474,000	610,103,000	(134,898,000)	$ (72,067,000)
Ending Balance (in shares) at Dec. 31, 2018	1,672,917					1,672,917
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	$ 209,829,000	0	0		0	$ 0
Other comprehensive income	7,099,000	0	0	0	7,099,000	0
Cumulative Effect on Retained Earnings, Tax	0	0	0	23,094,000	(23,094,000)	0
Dividends (per share of common stock, $0.80)	(22,360,000)	$ 0	0	(22,360,000)	0	$ 0
Changes due to convertible notes transactions (in shares)		0				0
Changes due to convertible notes transactions		$ 0		0	0	$ 0
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature	(18,000)		(18,000)
Purchase of treasury shares (in shares)		0				522,622
Purchase of treasury shares	(31,785,000)	$ 0	0	0	0	$ (31,785,000)
Employee stock plans (in shares)		449,937
Employee stock plans	19,676,000	$ 449,000	20,151,000	0	0
Employee stock plans (in shares)						17,609
Employee stock plans						$ (924,000)
Share-based compensation expense (in shares)		63,804
Share-based compensation expense	7,604,000	$ 64,000	7,546,000	0	0
Share-based compensation expense (in shares)						6,184
Share-based compensation expense						$ (6,000)
Ending Balance (in shares) at Dec. 31, 2019		30,058,455
Ending Balance at Dec. 31, 2019	$ 823,202,000	$ 30,058,000	$ 228,153,000	$ 820,666,000	$ (150,893,000)	$ (104,782,000)
Ending Balance (in shares) at Dec. 31, 2019	2,219,332					2,219,332