FINANCING ARRANGEMENTS (Details) $ / shares in Units, shares in Millions			1 Months Ended	9 Months Ended
	Jul. 20, 2018 USD ($) $ / shares	Mar. 30, 2018 USD ($)	May 31, 2015 USD ($) $ / shares shares	Nov. 30, 2018 USD ($) Note	Feb. 28, 2018 USD ($)
Debt Instrument [Line Items]
Loss on extinguishment of debt				$ 2,033,000
Repurchase of common stock				39,000,000
Issuance costs attributable to the liability component				$ 7,305,000
Convertible Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Number of outstanding convertible senior unsecured notes | Note				2
2020 Convertible Notes [Member]
Debt Instrument [Line Items]
Aggregate principal amount				$ 122,527,000	$ 172,500,000
Debt instrument, face amount			$ 172,500,000
Interest rate (as a percent)			1.625%
Maturity date			May 15, 2020
Conversion rate of shares of common stock			36.2398
Conversion price (in dollars per share) | $ / shares			$ 27.594
Percentage of repurchase price of the principal amount			100.00%
Maximum number of shares of common stock that could be issued, following certain corporate events that occur prior to maturity | shares			2.5
Aggregate amount of notes repurchase	$ 50,000,000
Repurchases of notes including accrued interest	53,800,000
Allocated notes repurchase price	53,700,000
Notes repurchase price, fair value of liability	47,600,000			119,200,000
Notes repurchase price, equity component	6,100,000
Carrying value of repurchased notes	45,600,000
Loss on extinguishment of debt	2,000,000
Issuance costs				979,000	2,058,000
Debt discount to be amortized				$ 7,748,000	$ 16,143,000
2020 Convertible Notes [Member] | Additional Paid-in Capital [Member]
Debt Instrument [Line Items]
Proceeds from unwind of the note hedge and warrants	$ 3,100,000
2020 Convertible Notes [Member] | Discount Rate [Member]
Debt Instrument [Line Items]
Market interest rate used to discount nonconvertible debt	0.0436			0.062
2025 Convertible Notes [Member]
Debt Instrument [Line Items]
Aggregate principal amount				$ 230,000,000
Debt instrument, face amount	$ 230,000,000
Interest rate (as a percent)	2.00%
Maturity date	Aug. 01, 2025
Conversion rate of shares of common stock	32.5256
Conversion price (in dollars per share) | $ / shares	$ 30.7450
Notes repurchase price, fair value of liability				199,600,000
Proceeds from sale of notes	$ 222,700,000
Issuance costs	7,300,000			4,920,000
Amount utilized from net proceeds of offering	90,000,000
Payment for capped call transactions	21,200,000			21,200,000
Repurchase of common stock	15,000,000
Principal of notes allocated to debt	160,800,000
Principal of notes allocated to stockholders equity	$ 69,200,000
Discount rate (as a percent)	0.0756
Debt Instrument, Measurement Input [Extensible List]	us-gaap:MeasurementInputDiscountRateMember
Deferred tax effect of conversion feature	$ 17,300,000
Debt discount to be amortized	$ 69,200,000			66,460,000
Effective interest rate	7.56%
Issuance costs attributable to the liability component	$ 5,100,000
Equity component of issuance costs	2,200,000
Deferred tax asset related to notes issuance	$ 500,000			$ 5,300,000
2025 Convertible Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Conversion rate of shares of common stock				41.3875
Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 50,000,000
Maturity date		Mar. 30, 2020
Borrowings outstanding				$ 0