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, 2013		27,189,922
Beginning Balance at Dec. 31, 2013	$ 511,292	$ 27,190	$ 133,517	$ 439,441	$ (81,121)	$ (7,735)
Beginning Balance (in shares) at Dec. 31, 2013						330,487
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	57,872			57,872
Other comprehensive income	(45,140)				(45,140)
Dividends	(17,329)			(17,329)
Purchase of treasury shares (in shares)						21,312
Purchase of treasury shares	(853)					$ (853)
Employee stock plans (in shares)		235,233
Employee stock plans	6,412	$ 235	6,992
Employee stock plans (in shares)						16,352
Employee stock plans						$ (815)
Share-based compensation expense (in shares)		93,071
Share-based compensation expense	5,411	$ 93	5,336
Share-based compensation expense (in shares)						17,791
Share-based compensation expense						$ (18)
Ending Balance (in shares) at Dec. 31, 2014		27,518,226
Ending Balance at Dec. 31, 2014	517,665	$ 27,518	145,845	479,984	(126,261)	$ (9,421)
Ending 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					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)
Amounts reclassified to temporary equity	(1,797)		(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