FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands	Jun. 30, 2011	Mar. 31, 2011
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	$ 386,267	$ 469,288
U.S. Treasury Bills and Government Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	105,350	198,246
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	61,688	154,703
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	43,662	43,543
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]
Available-for-sale Securities, Fair Value Disclosure	0	0
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	55,776	52,568
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
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	55,776	52,568
Commercial Paper [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] | Fair Value, Measurements, Recurring [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	55,016	33,358
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
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	55,016	33,358
Corporate Bonds [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] | Fair Value, Measurements, Recurring [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Available-for-sale Securities, Fair Value Disclosure	7,399	10,312
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
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	7,399	10,312
Certificates of Deposit [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
Derivative Assets [Member] | Fair Value, Measurements, Recurring [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	777	360
Derivative 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
Derivative Assets [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative assets	777	360
Derivative 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
Derivative Liabilities [Member] | Fair Value, Measurements, Recurring [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	3,316	4,201
Derivative Liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	37	27
Derivative Liabilities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Derivative liabilities	3,279	4,174
Derivative 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
Cash [Member] | Fair Value, Measurements, Recurring [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	121,226	136,804
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	121,226	136,804
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 [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
Money Market Accounts [Member] | Fair Value, Measurements, Recurring [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	41,500	38,000
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	41,500	38,000
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
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
Fair Value, Measurements, Recurring [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Total assets measured at fair value	387,044	469,648
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	224,414	329,507
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	162,630	140,141
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