FINANCING ARRANGEMENTS (Details)				1 Months Ended			3 Months Ended
	Jul. 20, 2018 USD ($)	Mar. 30, 2018 USD ($)	Apr. 30, 2015 $ / shares	Jul. 31, 2018 USD ($) shares	May 31, 2016 USD ($) shares	May 31, 2015 USD ($) shares	May 31, 2019 USD ($) Note	Apr. 12, 2019 USD ($)	Feb. 28, 2019 USD ($)
Debt Instrument [Line Items]
Long-term debt							$ 298,371,000		$ 275,905,000
Synovia Solutions LLC (“Synovia”) [Member]
Debt Instrument [Line Items]
Percentage of subscription contract value on sales price paid								80.00%
Fair value of debt								$ 20,100,000
Pre-tax cost of debt percentage								4.70%
Unamortized discount								$ 300,000
Interest expense related to debt recognized							$ 100,000
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							$ 122,500,000
Debt instrument, face amount						$ 172,500,000
Interest rate (as a percent)						1.625%
Maturity date						May 15, 2020
Minimum percentage of aggregate principal by holders						25.00%
Percentage of repurchase price of the principal amount						100.00%
Indebtedness for excess money borrowed						$ 10,000,000
Indebtedness, entry of judgments for payment						$ 10,000,000
Debt instrument, covenant description						The 2020 Indenture contains customary terms and conditions, including that upon certain events of default occurring and continuing, either the Trustee or the holders of at least 25% in aggregate principal amount of the then outstanding Notes, by notice to us and the Trustee, may declare 100% of the principal amount of, and accrued and unpaid interest, if any, on all the 2020 Convertible Notes then outstanding to be due and payable immediately. Such events of default include, without limitation, the default by us or any of our subsidiaries with respect to indebtedness for borrowed money in excess of $10 million and the entry of judgments for the payment of $10 million or more against us or any of our subsidiaries which are not paid, discharged or stayed within 60 days.
Maximum number of shares of common stock that could be issued, following certain corporate events that occur prior to maturity | shares						2,500,000
Number of common stock with hedge transactions | shares					6,250,000
Payments for notes hedges					$ 31,300,000
Purchase of note hedges, net of tax					$ 19,300,000
Warrants will be exercisable in equal installments							80 days
Proceeds from issuance of warrants							$ 16,000,000
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						$ 119,400,000
Notes repurchase price, equity component	6,100,000
Carrying value of repurchased notes	45,600,000
Loss on extinguishment of debt	$ 2,000,000
Conversion rate of shares of common stock							36.2398
Long-term debt							$ 116,706,000		115,249,000
2020 Convertible Notes [Member] | Discount Rate [Member]
Debt Instrument [Line Items]
Market interest rate used to discount nonconvertible debt	0.0436
2020 Convertible Notes [Member] | Warrant [Member]
Debt Instrument [Line Items]
Strike price of underlie convertible notes (in dollars per share) | $ / shares			$ 39.42
Percentage of premium on sale price of common stock			100.00%
Share price (in dollars per share) | $ / shares			$ 19.71
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] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, default judgment payment period						60 days
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
Indebtedness for excess money borrowed	$ 10,000,000
Indebtedness, entry of judgments for payment	$ 15,000,000
Debt instrument, covenant description							The 2025 Indenture contains customary terms and conditions, including that upon certain events of default occurring and continuing, either the Trustee, by notice to us, or the holders of at least 25% in aggregate principal amount of the then outstanding Notes, by notice to us and the Trustee, may declare the principal amount of, and all accrued and unpaid interest on, all of the 2025 Convertible Notes then outstanding to become due and payable immediately. Such events of default include, without limitation, the default by us or any of our subsidiaries with respect to indebtedness for borrowed money in excess of $10 million and the entry of judgments for the payment of $15 million or more against us or any of our subsidiaries, which are not paid, discharged or stayed within 60 days.
Number of common stock with hedge transactions | shares				7,480,000
Payments for notes hedges				$ 21,200,000
Purchase of note hedges, net of tax				$ 15,900,000
Notes repurchase price, fair value of liability							$ 176,400,000
Debt instrument, redemption, description							We may redeem the Notes at our option at any time on or after August 6, 2022 at a cash redemption price equal to the principal amount plus accrued interest, but only if the last reported sale price per share of our stock exceeds 130% of the conversion price on (i) each of at least 20 trading days, whether or not consecutive, during the 30 consecutive trading days ending on, and including, the trading day immediately before the date we send the related redemption notice; and (ii) the trading day immediately before the date we send such notice.
Conversion rate of shares of common stock				41.3875			32.5256
Long-term debt							$ 162,839,000		$ 160,656,000
2025 Convertible Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, default judgment payment period	60 days
Due to Factors [Member]
Debt Instrument [Line Items]
Long-term debt							18,826,000
Due to Factors [Member] | Synovia Solutions LLC (“Synovia”) [Member]
Debt Instrument [Line Items]
Long-term debt								$ 19,800,000
Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 50,000,000
Maturity date		Mar. 30, 2020
Borrowings outstanding							$ 0