FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands	Sep. 30, 2011	Mar. 31, 2011
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	$ 348,989	$ 469,288
Cash [Member] | Cash and Cash Equivalents [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	168,875	136,804
Cash [Member] | Cash and Cash Equivalents [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Cash [Member] | Cash and Cash Equivalents [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Cash [Member] | Cash and Cash Equivalents [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	168,875	136,804
Cash and Cash Equivalents [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	74,991
Cash and Cash Equivalents [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	5,004	7,002
Cash and Cash Equivalents [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Cash and Cash Equivalents [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	5,004	81,993
Cash and Cash Equivalents [Member] | Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Cash and Cash Equivalents [Member] | Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	4,998	22,495
Cash and Cash Equivalents [Member] | Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Cash and Cash Equivalents [Member] | Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	4,998	22,495
Cash and Cash Equivalents [Member] | Money Market Accounts [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	6,500	38,000
Cash and Cash Equivalents [Member] | Money Market Accounts [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Cash and Cash Equivalents [Member] | Money Market Accounts [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Cash and Cash Equivalents [Member] | Money Market Accounts [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	6,500	38,000
Cash and Cash Equivalents [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0
Cash and Cash Equivalents [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		3,082
Cash and Cash Equivalents [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0
Cash and Cash Equivalents [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		3,082
Cash and Cash Equivalents [Member] | Certificates of Deposit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0
Cash and Cash Equivalents [Member] | Certificates of Deposit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		2,001
Cash and Cash Equivalents [Member] | Certificates of Deposit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure
Cash and Cash Equivalents [Member] | Certificates of Deposit [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		2,001
U.S. Treasury Bills and Government Agency Securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	62,011	98,861
U.S. Treasury Bills and Government Agency Securities [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	34,016	71,756
U.S. Treasury Bills and Government Agency Securities [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	27,995	27,105
U.S. Treasury Bills and Government Agency Securities [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
U.S. Treasury Bills and Government Agency Securities [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	62,011	98,861
U.S. Treasury Bills and Government Agency Securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	21,055	17,391
U.S. Treasury Bills and Government Agency Securities [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	7,955
U.S. Treasury Bills and Government Agency Securities [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	21,055	9,436
U.S. Treasury Bills and Government Agency Securities [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
U.S. Treasury Bills and Government Agency Securities [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	21,055	17,391
Corporate Bonds [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	22,064	11,216
Corporate Bonds [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Corporate Bonds [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	22,064	11,216
Corporate Bonds [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Corporate Bonds [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	22,064	11,216
Corporate Bonds [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	33,084	19,059
Corporate Bonds [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Corporate Bonds [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	33,084	19,059
Corporate Bonds [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Corporate Bonds [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	33,084	19,059
Certificates of Deposit [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	2,518	5,429
Certificates of Deposit [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Certificates of Deposit [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	2,518	5,429
Certificates of Deposit [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Certificates of Deposit [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	2,518	5,429
Certificates of Deposit [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	4,891	2,882
Certificates of Deposit [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Certificates of Deposit [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	4,891	2,882
Certificates of Deposit [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Certificates of Deposit [Member] | Long Term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	4,891	2,882
Commercial Paper [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Commercial Paper [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	17,989	30,075
Commercial Paper [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Commercial Paper [Member] | Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	17,989	30,075
Other Current Assets [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	0	0
Other Current Assets [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	2,619	360
Other Current Assets [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	0	0
Other Current Assets [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	2,619	360
Accrued Liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	23	27
Accrued Liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	2,292	4,174
Accrued Liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	0	0
Accrued Liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	2,315	4,201
Commercial Paper [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	17,989	30,075
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	209,391	329,506
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	142,217	140,142
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	$ 351,608	$ 469,648