Basis of Presentation and Summary of Significant Accounting Policies (Details) (USD $)	3 Months Ended
	Jun. 30, 2012 Auction rate securities	Jun. 30, 2012 Recurring basis Total	Dec. 31, 2011 Recurring basis Total	Jun. 30, 2012 Recurring basis Total Money market funds	Dec. 31, 2011 Recurring basis Total Money market funds	Jun. 30, 2012 Recurring basis Total Corporate debt securities	Dec. 31, 2011 Recurring basis Total Corporate debt securities	Jun. 30, 2012 Recurring basis Total U.S. treasury and government agency securities	Dec. 31, 2011 Recurring basis Total U.S. treasury and government agency securities	Jun. 30, 2012 Recurring basis Total Commercial paper	Dec. 31, 2011 Recurring basis Total Commercial paper	Dec. 31, 2011 Recurring basis Total Auction rate securities	Jun. 30, 2012 Recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1)	Dec. 31, 2011 Recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1)	Jun. 30, 2012 Recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1) Money market funds	Dec. 31, 2011 Recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1) Money market funds	Jun. 30, 2012 Recurring basis Significant Other Observable Inputs (Level 2)	Dec. 31, 2011 Recurring basis Significant Other Observable Inputs (Level 2)	Jun. 30, 2012 Recurring basis Significant Other Observable Inputs (Level 2) Corporate debt securities	Dec. 31, 2011 Recurring basis Significant Other Observable Inputs (Level 2) Corporate debt securities	Jun. 30, 2012 Recurring basis Significant Other Observable Inputs (Level 2) U.S. treasury and government agency securities	Dec. 31, 2011 Recurring basis Significant Other Observable Inputs (Level 2) U.S. treasury and government agency securities	Jun. 30, 2012 Recurring basis Significant Other Observable Inputs (Level 2) Commercial paper	Dec. 31, 2011 Recurring basis Significant Other Observable Inputs (Level 2) Commercial paper	Dec. 31, 2011 Recurring basis Significant Unobservable Inputs (Level 3)	Dec. 31, 2011 Recurring basis Significant Unobservable Inputs (Level 3) Auction rate securities
Fair value of assets measured on a recurring basis
Fair value of assets		$ 203,988,000	$ 222,225,000	$ 27,417,000	$ 55,995,000	$ 110,218,000	$ 94,626,000	$ 58,876,000	$ 48,086,000	$ 7,477,000	$ 5,991,000	$ 17,527,000	$ 27,417,000	$ 55,995,000	$ 27,417,000	$ 55,995,000	$ 176,571,000	$ 148,703,000	$ 110,218,000	$ 94,626,000	$ 58,876,000	$ 48,086,000	$ 7,477,000	$ 5,991,000	$ 17,527,000	$ 17,527,000
Aggregate par value of auction rate securities sold during the period	19,800,000
Proceeds from the sale of ARS holdings	$ 18,300,000