ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES - Income statement (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	$ 229,125	$ 196,109	$ 616,132	$ 537,654
Cost of goods sold	109,049	98,568	303,152	282,354
Gross profit	120,076	97,541	312,980	255,300
Selling, general, and administrative expenses	86,071	69,417	235,191	190,746
Operating income	34,005	28,124	77,789	64,554
Interest expense	(5,319)	(7,755)	(17,081)	(24,474)
Other expense	(304)	(214)	(192)	(325)
Income before income taxes	28,382	20,155	60,516	39,755
Income tax expense	(7,080)	(3,125)	(14,824)	(7,161)
Net income	21,302	$ 17,030	45,692	$ 32,594
Impact of Adoption | No. 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	(754)		(7,033)
Cost of goods sold	45		(2,433)
Gross profit	(799)		(4,600)
Selling, general, and administrative expenses	84		319
Operating income	(883)		(4,919)
Income before income taxes	(883)		(4,919)
Income tax expense	216		1,206
Net income	(667)		(3,713)
Balances without Adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	228,371		609,099
Cost of goods sold	109,094		300,719
Gross profit	119,277		308,380
Selling, general, and administrative expenses	86,155		235,510
Operating income	33,122		72,870
Interest expense	(5,319)		(17,081)
Other expense	(304)		(192)
Income before income taxes	27,499		55,597
Income tax expense	(6,864)		(13,618)
Net income	$ 20,635		$ 41,979