FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	$ 254,023	$ 216,883
Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	173,260	175,634
Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	427,283	392,517
U.S. Treasury Bills and Government Agency Securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	55,358	29,837
Corporate Bonds
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	23,898	25,510
Certificates of Deposit
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,005	0
U.S. Treasury Bills and Government Agency Securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	66,107	61,896
Commercial Paper
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	15,679	20,039
Corporate Bonds
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	34,795	38,356
Certificates of Deposit
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	4,886
Cash and cash equivalents | Cash | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	118,881	147,338
Cash and cash equivalents | Cash | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Cash and cash equivalents | Cash | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	118,881	147,338
Cash and cash equivalents | U.S. Treasury Bills and Government Agency Securities | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	104,995	50,000
Cash and cash equivalents | U.S. Treasury Bills and Government Agency Securities | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Cash and cash equivalents | U.S. Treasury Bills and Government Agency Securities | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	104,995	50,000
Cash and cash equivalents | Commercial Paper | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Cash and cash equivalents | Commercial Paper | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	4,900	11,997
Cash and cash equivalents | Commercial Paper | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	4,900	11,997
Short-term Investments | U.S. Treasury Bills and Government Agency Securities | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	7,243	12,898
Short-term Investments | U.S. Treasury Bills and Government Agency Securities | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	58,864	48,998
Short-term Investments | U.S. Treasury Bills and Government Agency Securities | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	66,107	61,896
Short-term Investments | Commercial Paper | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Short-term Investments | Commercial Paper | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	15,679	20,039
Short-term Investments | Commercial Paper | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	15,679	20,039
Short-term Investments | Corporate Bonds | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Short-term Investments | Corporate Bonds | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	34,795	38,356
Short-term Investments | Corporate Bonds | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	34,795	38,356
Short-term Investments | Certificates of Deposit | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure		0
Short-term Investments | Certificates of Deposit | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure		4,886
Short-term Investments | Certificates of Deposit | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure		4,886
Long Term Investments | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0
Long Term Investments | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,005
Long Term Investments | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	1,005
Long Term Investments | U.S. Treasury Bills and Government Agency Securities | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	22,904	6,647
Long Term Investments | U.S. Treasury Bills and Government Agency Securities | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	32,454	23,190
Long Term Investments | U.S. Treasury Bills and Government Agency Securities | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	55,358	29,837
Long Term Investments | Corporate Bonds | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	0	0
Long Term Investments | Corporate Bonds | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	23,898	25,510
Long Term Investments | Corporate Bonds | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	23,898	25,510
Other Current Assets | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	0	0
Other Current Assets | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	1,665	2,658
Other Current Assets | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	1,665	2,658
Accrued Liabilities | Fair Value, Measurements, Recurring | Level 1
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	3	7
Accrued Liabilities | Fair Value, Measurements, Recurring | Level 2
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	291	714
Accrued Liabilities | Fair Value, Measurements, Recurring | Total
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	$ 294	$ 721