STOCK BASED COMPENSATION - Balances of stock-based compensation plans (Details) shares in Thousands	6 Months Ended
	Jun. 29, 2019 $ / shares shares
Stock options
Number of Options
Balance at the beginning | shares	2,889
Granted | shares	541
Exercise of options | shares	(624)
Forfeited/expired | shares	(50)
Balance at the end | shares	2,756
Weighted Average Exercise Price
Balance at the beginning (in dollars per share) | $ / shares	$ 6.56
Granted (per share) | $ / shares	22.84
Exercised/released | $ / shares	3.31
Forfeited/expired | $ / shares	19.58
Balance at the end (in dollars per share) | $ / shares	$ 10.26
Performance-based RSU
Number of RSUs
Balance at the beginning | shares	1,411
Forfeited/expired | shares	(93)
Balance at the end | shares	1,318
Weighted Average Grant Date Fair Value
Balance at the beginning (in dollars per share) | $ / shares	$ 31.74
Forfeited/expired (in dollars per share) | $ / shares	31.74
Balance at the end (in dollars per share) | $ / shares	$ 31.74
Restricted stock units (RSUs)
Number of RSUs
Balance at the beginning | shares	7
Granted | shares	307
Forfeited/expired | shares	(12)
Balance at the end | shares	302
Weighted Average Grant Date Fair Value
Balance at the beginning (in dollars per share) | $ / shares	$ 17.00
Granted (in dollars per share) | $ / shares	23.02
Forfeited/expired (in dollars per share) | $ / shares	22.84
Balance at the end (in dollars per share) | $ / shares	$ 22.89
Deferred stock units
Number of RSUs
Balance at the beginning | shares	13
Granted | shares	10
Balance at the end | shares	23
Weighted Average Grant Date Fair Value
Balance at the beginning (in dollars per share) | $ / shares	$ 17.00
Granted (in dollars per share) | $ / shares	24.80
Balance at the end (in dollars per share) | $ / shares	$ 20.34