INCOME TAXES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income before income tax expense
U.S. operations	$ 77,996	$ 61,353	$ 32,328
Foreign operations	25,423	14,397	6,574
Income before income tax expense	103,419	75,750	38,902
Current:
Federal	24,988	20,154	6,665
State	6,101	4,472	1,903
Foreign	6,224	4,808	3,621
Total current	37,313	29,434	12,189
Deferred:
Federal	(1,098)	(1,315)	4,135
State	505	753	607
Foreign	751	293	(1,213)
Total deferred	158	(269)	3,529
Income tax expense	37,471	29,165	$ 15,718
Deferred tax assets
Accounts receivable, principally due to allowance for doubtful accounts	2,949	2,750
Inventories	4,707	3,883
Net operating loss carryforwards	7,260	8,626
Accrued pension	25,939	27,598
Stock-based compensation	5,813	5,794
Compensation-related accruals	5,131	4,218
Warranty	3,245	2,893
Obligation for postretirement benefits other than pension	2,131	3,706
Accrued liabilities and other items	8,195	9,247
Gross deferred tax assets	65,370	68,715
Valuation allowance	(6,317)	(7,901)
Net deferred tax assets	59,053	60,814
Deferred tax liabilities:
Intangibles	84,931	86,464
Plant and equipment	29,596	22,685
Gross deferred tax liabilities	114,527	109,149
Net deferred tax liabilities	$ (55,474)	$ (48,335)