STOCKHOLDERS' EQUITY - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Changes in accumulated other comprehensive income (loss), net of tax
Beginning Balance	$ (43,774)	$ (43,403)	$ (37,318)
Before-Tax Amount	(19,368)	(1,396)	(10,297)
Tax Benefit (Expense)	(491)	1,025	4,212
Total other comprehensive loss, net of tax	(19,859)	(371)	(6,085)
Ending Balance	(68,394)	(43,774)	(43,403)
Pension and other post-employment liability adjustment
Changes in accumulated other comprehensive income (loss), net of tax
Beginning Balance	(38,163)	(29,405)	(22,832)
Before-Tax Amount	3,575	(9,783)	(10,785)
Tax Benefit (Expense)	(930)	1,025	4,212
Total other comprehensive loss, net of tax	2,645	(8,758)	(6,573)
Ending Balance	(40,279)	(38,163)	(29,405)
Interest rate swap derivative
Changes in accumulated other comprehensive income (loss), net of tax
Beginning Balance	0
Before-Tax Amount	(1,689)
Tax Benefit (Expense)	439
Total other comprehensive loss, net of tax	(1,250)
Ending Balance	(1,250)	0
Foreign currency translation adjustment
Changes in accumulated other comprehensive income (loss), net of tax
Beginning Balance	(5,611)	(13,998)	(14,486)
Before-Tax Amount	(13,140)	8,387	488
Tax Benefit (Expense)	0	0	0
Total other comprehensive loss, net of tax	(13,140)	8,387	488
Ending Balance	(18,751)	(5,611)	$ (13,998)
Foreign currency translation adjustment on long-term intercompany notes
Changes in accumulated other comprehensive income (loss), net of tax
Beginning Balance	0
Before-Tax Amount	(8,114)
Tax Benefit (Expense)	0
Total other comprehensive loss, net of tax	(8,114)
Ending Balance	$ (8,114)	$ 0
ASU 2018-02
Changes in accumulated other comprehensive income (loss), net of tax
ASU 2018-02				$ (4,761)
ASU 2018-02 | Pension and other post-employment liability adjustment
Changes in accumulated other comprehensive income (loss), net of tax
ASU 2018-02				$ (4,761)