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CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Mar. 31, 2012
Jun. 30, 2011
Mar. 31, 2011
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Cash and Cash Equivalents, Fair Value $ 204,639 $ 209,335 $ 197,726 $ 277,373
Cash, Cash Equivalents Before Unrealized Gains And Losses, and Amortized Cost Basis of Available-For-Sale Securities 384,583 389,777    
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Gains 135 141    
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Losses (35) (59)    
Cash and Fair Value of Cash Equivalents and Available-For-Sale Securities 384,683 389,859    
Available for Sale Securities, Debt Maturities [Abstract]        
Due in 1 year or less (amortized cost) 195,473 187,118    
Due in 1 to 3 years (amortized cost) 29,264 55,321    
Due in 1 year or less (fair value) 195,527 187,174    
Due in 1 to 3 years (fair value) 29,310 55,347    
Total amortized cost 224,737 242,439    
Total fair value 224,837 242,521    
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 10,146 29,814    
Available-for-sale securities, gross unrealized gains 9 24    
Available-for-sale securities, gross unrealized losses (2) (1)    
Available-for-sale securities, fair value 10,153 29,837    
Corporate Bonds [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale securities, amortized cost basis 19,118 25,507    
Available-for-sale securities, gross unrealized gains 42 29    
Available-for-sale securities, gross unrealized losses (3) (26)    
Available-for-sale securities, fair value 19,157 25,510    
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 85,564 61,898    
Available-for-sale securities, gross unrealized gains 22 22    
Available-for-sale securities, gross unrealized losses (15) (24)    
Available-for-sale securities, fair value 85,571 61,896    
Commercial Paper [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale securities, amortized cost basis 14,124 20,041    
Available-for-sale securities, gross unrealized gains 6 1    
Available-for-sale securities, gross unrealized losses (1) (3)    
Available-for-sale securities, fair value 14,129 20,039    
Corporate Bonds [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale securities, amortized cost basis 46,111 38,300    
Available-for-sale securities, gross unrealized gains 53 60    
Available-for-sale securities, gross unrealized losses (14) (4)    
Available-for-sale securities, fair value 46,150 38,356    
Certificates of Deposit [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale securities, amortized cost basis 4,882 4,883    
Available-for-sale securities, gross unrealized gains 2 3    
Available-for-sale securities, gross unrealized losses 0 0    
Available-for-sale securities, fair value 4,884 4,886    
Cash [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Cash 159,846 147,338    
Cash Equivalents [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Cash Equivalents Before Unrealized Gains And Losses 44,792 61,996    
Cash Equivalents, Gross Unrealized Gains 1 2    
Cash Equivalents, Gross Unrealized Losses 0 (1)    
Cash equivalents, fair value 44,793 61,997    
Cash and cash equivalents [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Cash and Cash Equivalents Before Unrealized Gains And Losses 204,638 209,334    
Cash Equivalents, Gross Unrealized Gains 1 2    
Cash Equivalents, Gross Unrealized Losses 0 (1)    
Cash and Cash Equivalents, Fair Value 204,639 209,335    
Short-term Investments [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale securities, amortized cost basis 150,681 125,122    
Available-for-sale securities, gross unrealized gains 83 86    
Available-for-sale securities, gross unrealized losses (30) (31)    
Available-for-sale securities, fair value 150,734 125,177    
Long-term investments [Member]
       
Schedule of Cash, Cash Equivalents and Investments [Line Items]        
Available-for-sale securities, amortized cost basis 29,264 55,321    
Available-for-sale securities, gross unrealized gains 51 53    
Available-for-sale securities, gross unrealized losses (5) (27)    
Available-for-sale securities, fair value $ 29,310 $ 55,347