INCOME TAXES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income before income tax expense
U.S. operations	$ 62,609	$ 107,803	$ 77,996
Foreign operations	15,983	19,735	25,423
Income before income tax expense	78,592	127,538	103,419
Current:
Federal	11,712	11,980	24,988
State	2,404	2,840	6,101
Foreign	3,918	4,588	6,224
Total current	18,034	19,408	37,313
Deferred:
Federal	(20,595)	23,814	(1,098)
State	2,541	2,347	505
Foreign	(1,580)	(145)	751
Total deferred	(19,634)	26,016	158
Income tax (benefit) expense	(1,600)	45,424	$ 37,471
Deferred tax assets
Accounts receivable, principally due to allowance for doubtful accounts	858	2,985
Inventories	5,939	8,294
Net operating loss carryforwards	7,460	6,664
Accrued pension	5,591	7,637
Stock-based compensation	2,972	6,493
Compensation-related accruals	3,063	4,928
Warranty	1,779	3,222
Obligation for post-employment benefits other than pension	1,312	2,267
Accrued liabilities and other items	3,886	8,537
Gross deferred tax assets	32,860	51,027
Valuation allowance	(4,789)	(6,161)
Net deferred tax assets	28,071	44,866
Deferred tax liabilities:
Intangibles	(58,701)	(86,961)
Plant and equipment	(24,041)	(34,759)
Gross deferred tax liabilities	(82,742)	(121,720)
Net deferred tax liabilities	$ (54,671)	$ (76,854)