Investments (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Schedule of financial assets measured at fair value on a recurring basis
Total	$ 76,837		$ 71,589
Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	49,082	[1]	43,262	[1]
Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	9,481	[1]	14,977	[1]
Auction rate notes [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	1,436	[2]	1,436	[2]
Money Market Funds [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	9,704	[3]	4,725	[3]
Municipal Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	5,132	[1]	5,194	[1]
US Government Agencies Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	2,002	[1]	1,995	[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	9,704		4,725
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	0	[1]	0	[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	0	[1]	0	[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	0	[2]	0	[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	9,704	[3]	4,725	[3]
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	0	[1]	0	[1]
Quoted Prices in Active Markets for Identical Assets Level 1 [Member] | US Government Agencies Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	0	[1]	0	[1]
Significant Other Observable Inputs Level 2 [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	65,697		65,428
Significant Other Observable Inputs Level 2 [Member] | Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	49,082	[1]	43,262	[1]
Significant Other Observable Inputs Level 2 [Member] | Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	9,481	[1]	14,977	[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	0	[2]	0	[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	0	[3]	0	[3]
Significant Other Observable Inputs Level 2 [Member] | Municipal Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	5,132	[1]	5,194	[1]
Significant Other Observable Inputs Level 2 [Member] | US Government Agencies Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	2,002		1,995	[1]
Significant Unobservable Inputs Level 3 [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	1,436		1,436
Significant Unobservable Inputs Level 3 [Member] | Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	0	[1]	0	[1]
Significant Unobservable Inputs Level 3 [Member] | Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	0	[1]	0	[1]
Significant Unobservable Inputs Level 3 [Member] | Auction rate notes [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	1,436	[2]	1,436	[2]
Significant Unobservable Inputs Level 3 [Member] | Money Market Funds [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	0	[3]	0	[3]
Significant Unobservable Inputs Level 3 [Member] | Municipal Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	0	[1]	0	[1]
Significant Unobservable Inputs Level 3 [Member] | US Government Agencies Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	$ 0	[1]	$ 0	[1]

[1] Included in short-term investments

[2] Included in long-term investments

[3] Included in cash and cash equivalents