STOCK-BASED COMPENSATION - Compensation Awards (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock options
Number of outstanding options
Balance at the beginning of the period (in shares)	2,900
Granted (in shares)	0
Exercised (in shares)	(16)
Forfeited (in shares)	(1,244)
Balance at the end of the period (in shares)	1,640	2,900
Weighted-Average Exercise Price of Outstanding Options
Balance at the beginning of the period (in dollars per share)	$ 23.72
Granted (in dollars per share)	0.00
Exercised (in dollars per share)	11.81
Forfeited (in dollars per share)	23.63
Balance at the end of the period (in dollars per share)	$ 23.90	$ 23.72
Additional disclosures
Aggregate intrinsic value of options outstanding	$ 0.4
Aggregate intrinsic value of options exercisable	0.4
Total intrinsic value of options exercised			$ 0.5
Total estimated fair value of options vested	$ 3.8	$ 4.7	10.0
RSUs and PSUs
Number of outstanding RSUs and PSUs/RSAs and PSAs
Balance at the beginning of the period (in shares)	413
Granted (in shares)	255
Released RSUs and RSAs (in shares)	(278)
Forfeited (in shares)	(20)
Balance at the end of the period (in shares)	370	413
Weighted-Average Fair Value per Share at Grant
Balance at the beginning of the period (in dollars per share)	$ 15.29
Granted (in dollars per share)	11.38
Released RSUs and RSAs (in dollars per share)	15.88
Forfeited (in dollars per share)	12.62
Balance at the end of the period (in dollars per share)	$ 11.57	$ 15.29
Additional disclosures
Total estimated fair value of options vested	$ 2.6	$ 3.9	5.6
RSAs and PSAs
Number of outstanding RSUs and PSUs/RSAs and PSAs
Balance at the beginning of the period (in shares)	1,125
Granted (in shares)	774
Released RSUs and RSAs (in shares)	(412)
Forfeited (in shares)	(39)
Balance at the end of the period (in shares)	1,448	1,125
Weighted-Average Fair Value per Share at Grant
Balance at the beginning of the period (in dollars per share)	$ 13.67
Granted (in dollars per share)	9.53
Released RSUs and RSAs (in dollars per share)	14.87
Forfeited (in dollars per share)	13.19
Balance at the end of the period (in dollars per share)	$ 9.95	$ 13.67
Additional disclosures
Total estimated fair value of options vested	$ 6.3	$ 14.7	$ 22.3