Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Common Stock	Treasury Stock	Additional Paid-in Capital
Beginning balance at Dec. 31, 2015	$ 463,705	$ 344,197	$ (5,114)	$ 2,102	$ (74)	$ 122,594
Beginning balance (in shares) at Dec. 31, 2015				31,528,449	(1,089)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	55,972	55,972
Other comprehensive income, net of cumulative effect of accounting change	(1,735)		(1,735)
Dividends	(12,080)	(12,080)
Treasury shares purchased	(1,588)				$ (1,588)
Treasury shares purchased (in shares)					(24,912)
Shares and options issued under stock plans	16,759			$ 15	$ 1,662	15,082
Shares and options issued under stock plans and an income tax benefit (in shares)				229,412	26,001
Ending balance at Dec. 31, 2016	521,033	388,089	(6,849)	$ 2,117	$ 0	137,676
Ending balance (in shares) at Dec. 31, 2016				31,757,861	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	90,071	90,071
Other comprehensive income, net of cumulative effect of accounting change	5,150	(57)	5,207
Dividends	(13,464)	(13,464)
Treasury shares purchased	(1,905)				$ (1,905)
Treasury shares purchased (in shares)					(23,182)
Shares and options issued under stock plans	15,996			$ 18	$ 1,905	14,073
Shares and options issued under stock plans and an income tax benefit (in shares)				261,744	23,182
Ending balance at Dec. 31, 2017	616,881	464,639	(1,642)	$ 2,135	$ 0	151,749
Ending balance (in shares) at Dec. 31, 2017				32,019,605	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	78,573	78,573
Other comprehensive income, net of cumulative effect of accounting change	(1,960)		(1,960)
Dividends	(15,185)	(15,185)
Treasury shares purchased	(1,394)				$ (1,394)
Treasury shares purchased (in shares)					(16,755)
Shares and options issued under stock plans	14,703			$ 16	$ 1,338	13,349
Shares and options issued under stock plans and an income tax benefit (in shares)				236,604	16,049
Ending balance at Dec. 31, 2018	$ 691,618	$ 528,027	$ (3,602)	$ 2,151	$ (56)	$ 165,098
Ending balance (in shares) at Dec. 31, 2018				32,256,209	(706)