Equity (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Balance			$ 205,583				$ 205,583
Net earnings	$ 6,585			$ 6,152			12,067	$ 10,491
Foreign currency translation adjustments	(711)			(182)			(481)	(1,292)
Pension liability adjustment, net of tax							(347)
Balance	207,650						207,650
Common Stock [Member]
Balance	10,002	$ 9,995	10,057	10,160	$ 10,268	$ 10,162	10,057	10,162
Common stock issued under equity incentive plans, net of shares withheld for employee taxes and strike price		7	1	21	89	108
Restricted stock forfeited				(2)		(2)
Issuance of restricted stock	30		1	23	2
Shares purchased and retired	(91)		(64)		(199)
Balance	9,941	10,002	9,995	(10,202)	10,160	10,268	9,941	(10,202)
Capital in Excess Of Par Value [Member]
Balance	65,141	64,634	64,263	59,928	59,013	55,884	64,263	55,884
Purchase of noncontrolling interest				3,535
Common stock issued under equity incentive plans, net of shares withheld for employee taxes and strike price		142	6	152	463	2,776
Restricted stock forfeited				2		2
Issuance of restricted stock	(30)		(1)	(23)	(2)
Share-based compensation expense	371	365	366	344	454	351
Balance	65,482	65,141	64,634	(63,938)	59,928	59,013	65,482	(63,938)
Reinvested Earnings [Member]
Balance	151,853	152,740	152,835	143,921	151,080	150,350	152,835	150,350
Net earnings	6,585	1,514	3,968	6,276	1,626	2,987
Cash dividends declared	(2,395)	(2,401)	(2,299)	(2,323)	(2,395)	(2,257)
Shares purchased and retired	(2,110)		(1,764)		(6,390)
Balance	153,933	151,853	152,740	(147,874)	143,921	151,080	153,933	(147,874)
Accumulated Other Comprehensive Loss [Member]
Balance	(21,111)	(21,334)	(21,572)	(18,419)	(17,826)	(17,859)	(21,572)	(17,859)
Foreign currency translation adjustments	(711)	100	130	(24)	(711)	(85)
Pension liability adjustment, net of tax	116	123	108	116	118	118
Purchase of noncontrolling interest				(1,111)
Balance	$ (21,706)	$ (21,111)	$ (21,334)	19,438	(18,419)	(17,826)	$ (21,706)	19,438
Noncontrolling Interest [Member]
Balance				6,446	6,829	7,122		$ 7,122
Net earnings				(124)	(103)	(171)
Foreign currency translation adjustments				(158)	(280)	(34)
Cash dividends paid to noncontrolling interest						(88)
Purchase of noncontrolling interest				$ (6,164)
Balance					$ 6,446	$ 6,829