Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning Balance (in shares) at Dec. 31, 2014		27,518,226
Beginning Balance at Dec. 31, 2014	$ 517,665	$ 27,518	$ 145,845	$ 479,984	$ (126,261)	$ (9,421)
Beginning Balance (in shares) at Dec. 31, 2014						385,942
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	60,438			60,438
Other comprehensive income	(13,877)				(13,877)
Dividends	(19,557)			(19,557)
Purchase of treasury shares (in shares)						319,234
Purchase of treasury shares	(12,836)					$ (12,836)
Employee stock plans (in shares)		137,037
Employee stock plans	4,856	$ 137	4,649
Employee stock plans (in shares)						(8,857)
Employee stock plans						$ 70
Share-based compensation expense (in shares)		80,494
Share-based compensation expense	6,388	$ 81	6,309
Share-based compensation expense (in shares)						1,864
Share-based compensation expense						$ (2)
Ending Balance (in shares) at Dec. 31, 2015		27,735,757
Ending Balance at Dec. 31, 2015	543,077	$ 27,736	156,803	520,865	(140,138)	$ (22,189)
Ending Balance (in shares) at Dec. 31, 2015						698,183
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	58,854			58,854
Other comprehensive income	(16,255)				(16,255)
Dividends	(19,519)			(19,519)
Changes due to convertible notes transactions			(1,797)
Purchase of treasury shares (in shares)						316,545
Purchase of treasury shares	(13,792)					$ (13,792)
Employee stock plans (in shares)		344,221
Employee stock plans	9,533	$ 344	10,541
Employee stock plans (in shares)						(28,672)
Employee stock plans						$ (1,352)
Share-based compensation expense (in shares)		82,519
Share-based compensation expense	5,686	$ 82	5,615
Share-based compensation expense (in shares)						10,964
Share-based compensation expense						$ (11)
Ending Balance (in shares) at Dec. 31, 2016		28,162,497
Ending Balance at Dec. 31, 2016	$ 565,787	$ 28,162	171,162	560,200	(156,393)	$ (37,344)
Ending Balance (in shares) at Dec. 31, 2016	1,054,364					1,054,364
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	$ 49,826
Other comprehensive income	40,579				40,579
Dividends	(22,149)			(22,149)
Changes due to convertible notes transactions	1,797		1,797
Changes due to convertible notes transactions (in shares)		624,044
Changes due to convertible notes transactions	(1,958)	$ 624	(2,582)
Purchase of treasury shares (in shares)						218,235
Purchase of treasury shares	(11,552)					$ (11,552)
Employee stock plans (in shares)		265,886
Employee stock plans	7,370	$ 266	9,074
Employee stock plans (in shares)						39,647
Employee stock plans						$ (1,970)
Share-based compensation expense (in shares)		89,040
Share-based compensation expense	5,956	$ 89	5,881
Share-based compensation expense (in shares)						13,729
Share-based compensation expense						$ (14)
Ending Balance (in shares) at Dec. 31, 2017		29,141,467
Ending Balance at Dec. 31, 2017	$ 635,656	$ 29,141	$ 185,332	$ 587,877	$ (115,814)	$ (50,880)
Ending Balance (in shares) at Dec. 31, 2017	1,325,975					1,325,975