M. SHARE-BASED COMPENSATION - RESTRICTED STOCK UNITS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Maximum
Vesting period	10 years
Restricted stock units
Number of shares
Outstanding, beginning balance	517	152	21
Granted	510	497	156
Released	(289)	(122)	(19)
Cancelled/Forfeited	(31)	(10)	(6)
Outstanding, ending balance	707	517	152
Exercisable, ending balance	4
Vested and expected to vest	703
Weighted Average Share Price On Date Of Granted		$ 13.50	$ 13.62
Weighted Average Share Price on Date of Release	$ 60.87
Weighted Average Fair Value
Outstanding, beginning balance	14.79	11.20	18.22
Granted	38.87	15.73	11.06
Released	20.92	14.09	18.24
Cancelled/Forfeited	24.23	15.38	10.00
Outstanding, ending balance	$ 29.23	$ 14.79	$ 11.20
Aggregate Intrinsic Value [Abstract]
Aggregate intrinsic value, outstanding	$ 12,128	$ 2,611	$ 238
Granted	19,803	7,815	1,722
Released	17,579	1,644	257
Cancelled/Forfeited	1,181	180	99
Aggregate intrinsic value, outstanding	26,732	$ 12,128	$ 2,611
Exercisable, ending balance	140
Vested and expected to vest	$ 26,592