ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES - Income statement (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	$ 231,654	$ 206,288	$ 387,007	$ 341,545
Cost of goods sold	115,377	105,718	194,103	183,786
Gross profit	116,277	100,570	192,904	157,759
Selling, general, and administrative expenses	81,277	67,384	149,120	121,329
Operating income	35,000	33,186	43,784	36,430
Interest expense	(5,695)	(8,593)	(11,762)	(16,719)
Other income	49	(93)	112	(111)
Income before income taxes	29,354	24,500	32,134	19,600
Income tax expense	(7,131)	(5,675)	(7,744)	(4,036)
Net income	22,223	$ 18,825	24,390	$ 15,564
Impact of Adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	(2,235)		(6,279)
Cost of goods sold	(834)		(2,478)
Gross profit	(1,401)		(3,801)
Selling, general, and administrative expenses	83		235
Operating income	(1,484)		(4,036)
Income before income taxes	(1,484)		(4,036)
Income tax expense	364		990
Net income	(1,120)		(3,046)
Balances without Adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	229,419		380,728
Cost of goods sold	114,543		191,625
Gross profit	114,876		189,103
Selling, general, and administrative expenses	81,360		149,355
Operating income	33,516		39,748
Interest expense	(5,695)		(11,762)
Other income	49		112
Income before income taxes	27,870		28,098
Income tax expense	(6,767)		(6,754)
Net income	$ 21,103		$ 21,344