FAIR VALUE MEASUREMENTS (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Mar. 31, 2013
Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	$ 226,537	$ 254,023
Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	203,161	173,260
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	429,698	427,283
Cash and Cash Equivalents [Member] | Cash [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value	225,310	118,881
Cash and Cash Equivalents [Member] | Cash [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value	0	0
Cash and Cash Equivalents [Member] | Cash [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value	225,310	118,881
Cash and Cash Equivalents [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value	1,227
Cash and Cash Equivalents [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value	0
Cash and Cash Equivalents [Member] | Mutual Funds [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value	1,227
Cash and Cash Equivalents [Member] | Commercial Paper [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value	0	0
Cash and Cash Equivalents [Member] | Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value	8,997	4,900
Cash and Cash Equivalents [Member] | Commercial Paper [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value	8,997	4,900
Cash and Cash Equivalents [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value		104,995
Cash and Cash Equivalents [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value		0
Cash and Cash Equivalents [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents, fair value		104,995
Short-term Investments [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	0	7,243
Short-term Investments [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	19,232	58,864
Short-term Investments [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	19,232	66,107
Short-term Investments [Member] | Commercial Paper [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	0	0
Short-term Investments [Member] | Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	43,805	15,679
Short-term Investments [Member] | Commercial Paper [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	43,805	15,679
Short-term Investments [Member] | Corporate Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	0	0
Short-term Investments [Member] | Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	22,357	34,795
Short-term Investments [Member] | Corporate Bonds [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	22,357	34,795
Short-term Investments [Member] | Certificates of Deposit [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	0
Short-term Investments [Member] | Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	1,003
Short-term Investments [Member] | Certificates of Deposit [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	1,003
Long Term Investments [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	0	22,904
Long Term Investments [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	36,938	32,454
Long Term Investments [Member] | U.S. Treasury Bills and Government Agency Securities [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	36,938	55,358
Long Term Investments [Member] | Corporate Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	0	0
Long Term Investments [Member] | Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	69,862	23,898
Long Term Investments [Member] | Corporate Bonds [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value	69,862	23,898
Long Term Investments [Member] | Certificates of Deposit [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value		0
Long Term Investments [Member] | Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value		1,005
Long Term Investments [Member] | Certificates of Deposit [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale securities, fair value		1,005
Other Current Assets [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, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	967	1,665
Other Current Assets [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	967	1,665
Accrued Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	0	3
Accrued Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	3,841	291
Accrued Liabilities [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	$ 3,841	$ 294