Investments (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Schedule of financial assets measured at fair value on a recurring basis
Total	$ 77,094		$ 85,946
Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	36,626	[1]	36,957	[1]
Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	16,479	[1]	13,993	[1]
Auction rate notes [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	1,732	[2]	4,195	[2]
Money Market Funds [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	9,412	[3]	16,945	[3]
Municipal Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	12,845	[1]	13,856	[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	9,412		16,945
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	9,412	[3]	16,945	[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]
Significant Other Observable Inputs Level 2 [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	65,950		64,806
Significant Other Observable Inputs Level 2 [Member] | Corporate Debt Securities [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	36,626	[1]	36,957	[1]
Significant Other Observable Inputs Level 2 [Member] | Commercial Paper [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	16,479	[1]	13,993	[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	12,845	[1]	13,856	[1]
Significant Unobservable Inputs Level 3 [Member]
Schedule of financial assets measured at fair value on a recurring basis
Total	1,732		4,195
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	1,732	[2]	4,195	[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]

[1] Included in short-term investments

[2] Included in long-term investments

[3] Included in cash and cash equivalents