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CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2012
Mar. 31, 2011
Mar. 31, 2010
Mar. 31, 2009
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Cash and Cash Equivalents, at Carrying Value $ 209,335 $ 277,373 $ 349,961 $ 158,193
Cash, Cash Equivalents Before Unrealized Gains And Losses, and Amortized Cost Basis of Available-For-Sale Securities 389,777 469,277    
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Gains 141 51    
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Losses (59) (40)    
Cash and Fair Value of Cash Equivalents and Available-For-Sale Securities 389,859 469,288    
Available for Sale Securities, Debt Maturities [Abstract]        
Due in 1 year or less (amortized cost) 187,118 293,121    
Due in 1 to 3 years (amortized cost) 55,321 39,352    
Due in 1 year or less (fair value) 187,174 293,152    
Due in 1 to 3 years (fair value) 55,347 39,332    
Total amortized cost 242,439 332,473    
Total fair value 242,521 332,484    
Corporate Bond Securities [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale Securities, gross unrealized gains 29 8    
U.S. Treasury Bills and Government Agency Securities [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale Securities, amortized cost basis 29,814 17,387    
Available-for-sale Securities, gross unrealized gains 24 4    
Available-for-sale Securities, gross unrealized losses (1) 0    
Available-for-sale Securities, fair value 29,837 17,391    
Corporate Bonds [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale Securities, amortized cost basis 25,507 19,086    
Available-for-sale Securities, gross unrealized losses (26) (35)    
Available-for-sale Securities, fair value 25,510 19,059    
Certificates of Deposit [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale Securities, amortized cost basis 0 2,879    
Available-for-sale Securities, gross unrealized gains 0 3    
Available-for-sale Securities, gross unrealized losses 0 0    
Available-for-sale Securities, fair value 0 2,882    
U.S. Treasury Bills and Government Agency Securities [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale Securities, amortized cost basis 61,898 105,849    
Available-for-sale Securities, gross unrealized gains 22 17    
Available-for-sale Securities, gross unrealized losses (24) (3)    
Available-for-sale Securities, fair value 61,896 105,863    
Commercial Paper [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale Securities, amortized cost basis 20,041 30,071    
Available-for-sale Securities, gross unrealized gains 1 5    
Available-for-sale Securities, gross unrealized losses (3) (1)    
Available-for-sale Securities, fair value 20,039 30,075    
Corporate Bonds [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale Securities, amortized cost basis 38,300 11,212    
Available-for-sale Securities, gross unrealized gains 60 4    
Available-for-sale Securities, gross unrealized losses (4) 0    
Available-for-sale Securities, fair value 38,356 11,216    
Certificates of Deposit [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale Securities, amortized cost basis 4,883 5,420    
Available-for-sale Securities, gross unrealized gains 3 9    
Available-for-sale Securities, gross unrealized losses 0 0    
Available-for-sale Securities, fair value 4,886 5,429    
Cash [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Cash 147,338 136,804    
Cash Equivalents [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Cash Equivalents Before Unrealized Gains And Losses 61,996 140,569    
Cash Equivalents, Gross Unrealized Gains 2 1    
Cash Equivalents, Gross Unrealized Losses (1) (1)    
Cash Equivalents, at Carrying Value 61,997 140,569    
Cash and cash equivalents [Member] | Cash and cash equivalents [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Cash and Cash Equivalents Before Unrealized Gains And Losses 209,334 277,373    
Cash Equivalents, Gross Unrealized Gains 2 1    
Cash Equivalents, Gross Unrealized Losses (1) (1)    
Cash and Cash Equivalents, at Carrying Value 209,335 277,373    
Short-term Investments [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale Securities, amortized cost basis 125,122 152,552    
Available-for-sale Securities, gross unrealized gains 86 35    
Available-for-sale Securities, gross unrealized losses (31) (4)    
Available-for-sale Securities, fair value 125,177 152,583    
Long-term Investments [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale Securities, amortized cost basis 55,321 39,352    
Available-for-sale Securities, gross unrealized gains 53 15    
Available-for-sale Securities, gross unrealized losses (27) (35)    
Available-for-sale Securities, fair value $ 55,347 $ 39,332