FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013
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	$ 255,430	$ 254,023
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	189,020	173,260
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	444,450	427,283
U.S. Treasury Bills and Government Agency Securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	42,901	55,358
Corporate Bonds [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	41,999	23,898
Certificates of Deposit [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,004	1,005
U.S. Treasury Bills and Government Agency Securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	37,417	66,107
Commercial Paper [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	39,758	15,679
Corporate Bonds [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	24,435	34,795
Cash and Cash Equivalents [Member] | Cash [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	242,348	118,881
Cash and Cash Equivalents [Member] | Cash [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] | Cash [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	242,348	118,881
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		104,995
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		0
Cash and Cash Equivalents [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		104,995
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	13,995	4,900
Cash and Cash Equivalents [Member] | Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	13,995	4,900
Short-term Investments [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]
Available-for-sale Securities, Fair Value Disclosure	0	7,243
Short-term Investments [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]
Available-for-sale Securities, Fair Value Disclosure	37,417	58,864
Short-term Investments [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	37,417	66,107
Short-term Investments [Member] | Commercial Paper [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
Short-term Investments [Member] | Commercial Paper [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	39,758	15,679
Short-term Investments [Member] | Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	39,758	15,679
Short-term Investments [Member] | Corporate Bonds [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
Short-term Investments [Member] | Corporate Bonds [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	24,435	34,795
Short-term Investments [Member] | Corporate Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	24,435	34,795
Long Term Investments [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]
Available-for-sale Securities, Fair Value Disclosure	13,082	22,904
Long Term Investments [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]
Available-for-sale Securities, Fair Value Disclosure	29,819	32,454
Long Term Investments [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	42,901	55,358
Long Term Investments [Member] | Corporate Bonds [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
Long Term Investments [Member] | Corporate Bonds [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	41,999	23,898
Long Term Investments [Member] | Corporate Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	41,999	23,898
Long Term Investments [Member] | Certificates of Deposit [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,004	1,005
Long Term Investments [Member] | Certificates of Deposit [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
Long Term Investments [Member] | Certificates of Deposit [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	1,004	1,005
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	593	1,665
Other Current Assets [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	593	1,665
Accrued Liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	9	3
Accrued Liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	1,130	291
Accrued Liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	$ 1,139	$ 294