Investments (Details 1) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Schedule of financial assets measured at fair value on a recurring basis
Total	$ 88,099		$ 94,353
Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	36,728	[1]	26,436	[1]
Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	16,450	[1]	18,462	[1]
Auction rate notes [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	4,212	[2]	4,159	[2]
Money Market Funds [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	14,179	[3]	13,845	[3]
Certificates of Deposits [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total			19,047	[1]
Municipal Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	16,530	[1]	12,404	[1]
Quoted Prices in Active Markets for Identical Assets Level 1 [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	14,179		32,892
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		[1]		[1]
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		[1]		[1]
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		[2]		[2]
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	14,179	[3]	13,845	[3]
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			19,047	[1]
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		[1]		[1]
Significant Other Observable Inputs Level 2 [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	69,708		57,302
Significant Other Observable Inputs Level 2 [Member] | Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	36,728	[1]	26,436	[1]
Significant Other Observable Inputs Level 2 [Member] | Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	16,450	[1]	18,462	[1]
Significant Other Observable Inputs Level 2 [Member] | Auction rate notes [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total		[2]		[2]
Significant Other Observable Inputs Level 2 [Member] | Money Market Funds [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total		[3]		[3]
Significant Other Observable Inputs Level 2 [Member] | Certificates of Deposits [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total				[1]
Significant Other Observable Inputs Level 2 [Member] | Municipal Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	16,530	[1]	12,404	[1]
Significant Unobservable Inputs Level 3 [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	4,212		4,159
Significant Unobservable Inputs Level 3 [Member] | Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total		[1]		[1]
Significant Unobservable Inputs Level 3 [Member] | Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total		[1]		[1]
Significant Unobservable Inputs Level 3 [Member] | Auction rate notes [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	4,212	[2]	4,159	[2]
Significant Unobservable Inputs Level 3 [Member] | Money Market Funds [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total		[3]		[3]
Significant Unobservable Inputs Level 3 [Member] | Certificates of Deposits [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total				[1]
Significant Unobservable Inputs Level 3 [Member] | Municipal Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total		[1]		[1]

[1] Included in short-term investments

[2] Included in long-term investments

[3] Included in cash and cash equivalents