DEBT - Convertible Subordinated Notes (Details) - Convertible subordinated notes $ / shares in Units, $ in Millions		1 Months Ended
	Jul. 31, 2014 $ / shares $ / Item	Jul. 31, 2014 $ / shares $ / Item shares	Jan. 31, 2013 USD ($) Item $ / shares $ / Item shares	Dec. 31, 2016 USD ($)
Privately-negotiated capped call option
Debt
Cap price for the underlying number of shares (in dollars per share) | $ / Item	27.04	27.04
2023 Notes
Debt
Loan amount			$ 287.5
Proceeds from issuance of notes payable, net of debt issuance costs			$ 281.2
Interest rate (as a percent)			2.125%
Initial conversion, shares per $1,000 principal amount | shares | shares			35.9903
Adjusted conversion, shares per $1,000 principal amount | shares		50.5818
Conversion price of convertible notes into common stock (in dollars per share) | $ / shares	$ 19.77	$ 19.77	$ 27.79
Portion of debt retired, face value				$ 14.1
Portion of debt retired, carrying value				$ 13.9
2023 Notes | Privately-negotiated capped call option
Debt
Payments for capped call options			$ 36.8
Number of derivative instruments purchased | Item			2
Strike price for the underlying number of shares (in dollars per share) | $ / shares	$ 27.79	$ 19.77	$ 27.79
Cap price for the underlying number of shares (in dollars per share) | $ / Item	38.00	38.00	38.00
2023 Notes | Stock prices below $27.79 per share | Minimum
Debt
Net shares settlement payable to the entity | shares			0
2023 Notes | Stock prices above $38.00 per share | Maximum
Debt
Net shares settlement payable to the entity | shares			2,779,659