STOCK OPTION PLANS - Stock option activity (Details) - $ / shares	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Number of shares underlying options
Unvested, end of period	134,200
Stock option plans
Number of shares underlying options
Outstanding, beginning of period	248,314,000	647,074,000	647,074,000
Granted	80,000,000
Forfeited	(12,160,000)
Exercised	(1,000,000)	(202,044,000)
Outstanding, end of period	315,154,000	445,030,000	248,314,000	647,074,000
Exercisable, end of period	180,954,000	371,230,000
Unvested, end of period	134,200,000	73,800,000
Weighted average exercise prices
Outstanding, beginning of period	$ 12.80	$ 10.99	$ 10.99
Granted	21.00
Forfeited	11.24
Exercised	16.80	9.88
Outstanding, end of period	14.93	11.50	$ 12.80	$ 10.99
Exercisable, end of period	$ 11.66	$ 10.42
Unvested, end of period	19.35	16.91
Weighted average contractual term (in years)
Outstanding	5 years 8 months 9 days	2 years 11 months 16 days	4 years 11 months 16 days	2 years 9 months 29 days
Granted	9 years 9 months 4 days
Forfeited	2 years 1 month 17 days