Investments (Details 1) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of financial assets measured at fair value on a recurring basis
Total	$ 104,158	$ 140,034
Money Market Funds [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	20,143	55,912
Certificates of Deposits [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	23,023	23,071
Municipal Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	10,282	11,298
Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	29,865	33,396
Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	13,961	4,989
U.S. Agencies [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total		4,511
Auction rate notes [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	6,884	6,857
Quoted Prices in Active Markets for Identical Assets Level 1 [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	43,166	78,983
Quoted Prices in Active Markets for Identical Assets Level 1 [Member] | Money Market Funds [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	20,143	55,912
Quoted Prices in Active Markets for Identical Assets Level 1 [Member] | Certificates of Deposits [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	23,023	23,071
Quoted Prices in Active Markets for Identical Assets Level 1 [Member] | Municipal Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Quoted Prices in Active Markets for Identical Assets Level 1 [Member] | Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Quoted Prices in Active Markets for Identical Assets Level 1 [Member] | Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Quoted Prices in Active Markets for Identical Assets Level 1 [Member] | U.S. Agencies [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Quoted Prices in Active Markets for Identical Assets Level 1 [Member] | Auction rate notes [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Significant Other Observable Inputs Level 2 [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	54,108	54,194
Significant Other Observable Inputs Level 2 [Member] | Money Market Funds [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Significant Other Observable Inputs Level 2 [Member] | Certificates of Deposits [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Significant Other Observable Inputs Level 2 [Member] | Municipal Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	10,282	11,298
Significant Other Observable Inputs Level 2 [Member] | Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	29,865	33,396
Significant Other Observable Inputs Level 2 [Member] | Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	13,961	4,989
Significant Other Observable Inputs Level 2 [Member] | U.S. Agencies [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total		4,511
Significant Other Observable Inputs Level 2 [Member] | Auction rate notes [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Significant Unobservable Inputs Level 3 [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	6,884	6,857
Significant Unobservable Inputs Level 3 [Member] | Money Market Funds [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Significant Unobservable Inputs Level 3 [Member] | Certificates of Deposits [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Significant Unobservable Inputs Level 3 [Member] | Municipal Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Significant Unobservable Inputs Level 3 [Member] | Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Significant Unobservable Inputs Level 3 [Member] | Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Significant Unobservable Inputs Level 3 [Member] | U.S. Agencies [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total
Significant Unobservable Inputs Level 3 [Member] | Auction rate notes [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	$ 6,884	$ 6,857