DEBT - Convertible Subordinated Notes (Details) - 2023 Notes - Convertible subordinated notes $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2013 USD ($) item $ / shares $ / item shares	Dec. 31, 2016 USD ($) $ / shares $ / item shares
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	$ 27.79	$ 19.77
Portion of debt retired, face value		$ 14.1
Portion of debt retired, carrying value		13.9
Settlement amount for purchase of notes		11.6
Other (expense) income, net
Debt
Gain (Loss) on Repurchase of Debt Instrument		$ 2.3
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
Cap price for the underlying number of shares (in dollars per share) | $ / item	38.00	27.04
Amount received from capped call option		$ 0.6
Stock prices below $27.79 per share | Minimum
Debt
Net shares settlement payable to the entity | shares	0
Stock prices above $38.00 per share | Maximum
Debt
Net shares settlement payable to the entity | shares	2,779,659