STOCK‑BASED COMPENSATION - Summary Of Stock Option Activity (Details) - $ / shares		12 Months Ended
	Mar. 28, 2017	Dec. 31, 2017
Number of Shares
Outstanding beginning balance (in shares)		4,645,884
Granted (in shares)		793,738
Exercised (in shares)	(162,212)	(226,194)
Forfeited (in shares)		(5,148)
Expired (in shares)		0
Canceled (in shares)		(571,927)
Outstanding ending balance (in shares)		4,636,353
Exercisable ending balance (in shares)		3,847,763
Weighted Average Exercise Price
Outstanding beginning balance (in dollars per share)		$ 3.49
Granted (in dollars per share)		14.00
Exercised (in dollars per share)		3.96
Forfeited (in dollars per share)		14.00
Expired (in dollars per share)		0.00
Canceled (in dollars per share)		3.96
Outstanding ending balance (in dollars per share)		5.20
Exercisable ending balance (in dollars per share)		$ 3.39