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Certain Financial Statement Information (Details 10) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Mar. 31, 2012
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis $ 89,687 $ 113,846
Cash, cash equivalents and available-for-sale investments measured at fair value on recurring basis 89,687 113,846
Level 1 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash, cash equivalents and available-for-sale investments measured at fair value on recurring basis 57,915 72,243
Level 2 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash, cash equivalents and available-for-sale investments measured at fair value on recurring basis 31,772 41,603
Level 3 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash, cash equivalents and available-for-sale investments measured at fair value on recurring basis      
Cash [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash and cash equivalents measured at fair value on a recurring basis 9,902 15,057
Cash [Member] | Level 1 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash and cash equivalents measured at fair value on a recurring basis 9,902 15,057
Cash [Member] | Level 2 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash and cash equivalents measured at fair value on a recurring basis     
Cash cash equivalents and short term investments, measured at fair value on a recurring basis     
Cash [Member] | Level 3 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash and cash equivalents measured at fair value on a recurring basis      
Cash equivalents [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash and cash equivalents measured at fair value on a recurring basis 2,090 13,008
Cash equivalents [Member] | Level 1 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash and cash equivalents measured at fair value on a recurring basis 2,090 10,510
Cash equivalents [Member] | Level 2 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash and cash equivalents measured at fair value on a recurring basis    2,498
Cash equivalents [Member] | Level 3 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash and cash equivalents measured at fair value on a recurring basis      
U.S Treasury securities and agency bonds [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis 17,555 16,763
U.S Treasury securities and agency bonds [Member] | Level 1 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis 17,555 16,763
U.S Treasury securities and agency bonds [Member] | Level 2 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis      
U.S Treasury securities and agency bonds [Member] | Level 3 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis      
Corporate bonds [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis 20,574 23,407
Corporate bonds [Member] | Level 1 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash and cash equivalents measured at fair value on a recurring basis     
Cash cash equivalents and short term investments, measured at fair value on a recurring basis     
Corporate bonds [Member] | Level 2 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis 20,574 23,407
Corporate bonds [Member] | Level 3 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis      
Mortgage-backed and asset-backed securities [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis 4,314 7,611
Mortgage-backed and asset-backed securities [Member] | Level 1 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash and cash equivalents measured at fair value on a recurring basis     
Cash cash equivalents and short term investments, measured at fair value on a recurring basis     
Mortgage-backed and asset-backed securities [Member] | Level 2 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis 4,314 7,611
Mortgage-backed and asset-backed securities [Member] | Level 3 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis      
Closed-end bond funds [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis 28,368 29,913
Closed-end bond funds [Member] | Level 1 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis 28,368 29,913
Closed-end bond funds [Member] | Level 2 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis 0   
Closed-end bond funds [Member] | Level 3 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis      
Preferred stock [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis 6,884 8,087
Preferred stock [Member] | Level 1 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash and cash equivalents measured at fair value on a recurring basis     
Cash cash equivalents and short term investments, measured at fair value on a recurring basis     
Preferred stock [Member] | Level 2 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis 6,884 8,087
Preferred stock [Member] | Level 3 [Member]
   
Schedule of Cash, Cash Equivalents and Available-For-Sale Investments by Type of Instruments Measured at Fair Value on Recurring Basis    
Cash cash equivalents and short term investments, measured at fair value on a recurring basis