STOCK BASED COMPENSATION - Summary of stock options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
2012 Plan | Stock Options
Number of Options
Options outstanding at beginning (in shares)	2,889	2,884	3,498
Options granted (in shares)		761	77
Options exercised (in shares)	(1,730)	(560)	(156)
Options forfeited, cancelled (in shares)	(142)	(172)	(529)
Options expired (in shares)	0	(24)	(6)
Options outstanding at ending (in shares)		2,889	2,884	3,498
Options exercisable (in shares)	574
Weighted Average Exercise Price
Weighted average exercise price at beginning (in dollars per share)	$ 6.56	$ 5.22	$ 4.10
Options granted (in dollars per share)		18.00	53.51
Options exercised (in dollars per share)	2.06	0.47	0.65
Options forfeited, cancelled (in dollars per share)	20.88	47.91	5.71
Options expired (in dollars per share)	0	53.55	46.63
Weighted average exercise price at ending (in dollars per share)		$ 6.56	$ 5.22	$ 4.10
Options exercisable (in dollars per share)	$ 8.48
Weighted average remaining contractual term (Years)		6 years 5 months 23 days	6 years 1 month 6 days	5 years 11 months 26 days
Weighted average remaining contractual term of options exercisable (years)	6 years 6 months
Aggregate intrinsic value of options exercisable options	$ 15,210
Total intrinsic value of stock options exercised	46,700	$ 10,000	$ 5,500
Total fair value of stock options vested	$ 12,200	$ 15,200	$ 17,700
2018 Plan
Number of Options
Options granted (in shares)	601
2018 Plan | Stock Options
Number of Options
Options granted (in shares)	601
Weighted Average Exercise Price
Options granted (in dollars per share)	$ 23.59
2012 and 2018 Plans | Stock Options
Number of Options
Options outstanding at ending (in shares)	1,618
Weighted Average Exercise Price
Weighted average exercise price at ending (in dollars per share)	$ 16.44
Weighted average remaining contractual term (Years)	8 years 1 month 13 days
Aggregate intrinsic value of options outstanding options	$ 29,985