Investments and Fair Value Disclosures (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Summary of assets and liabilities measured at fair value on a recurring basis
Total cash equivalents and certificates of deposit	$ 54,165	$ 71,147
Total investments	109,973	97,749
Total cash equivalents, certificates of deposit and investments	164,138	168,896
Fair Value, Measurements, Recurring [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total cash equivalents and certificates of deposit	54,165	71,147
Total investments	109,973	97,749
Total cash equivalents, certificates of deposit and investments	164,138	168,896
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total cash equivalents and certificates of deposit	54,165	71,147
Total cash equivalents, certificates of deposit and investments	54,165	71,147
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total investments	109,973	97,749
Total cash equivalents, certificates of deposit and investments	109,973	97,749
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total cash equivalents and certificates of deposit
Total investments
Total cash equivalents, certificates of deposit and investments
Money market funds [Member] | Fair Value, Measurements, Recurring [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total cash equivalents and certificates of deposit	53,160	70,142
Money market funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total cash equivalents and certificates of deposit	53,160	70,142
Money market funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total cash equivalents and certificates of deposit
Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total cash equivalents and certificates of deposit	1,005	1,005
Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total cash equivalents and certificates of deposit	1,005	1,005
Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total cash equivalents and certificates of deposit
U.S. agency notes [Member] | Fair Value, Measurements, Recurring [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total investments	48,699	27,672
U.S. agency notes [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total investments	48,699	27,672
U.S. agency notes [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total investments
Commercial paper [Member] | Fair Value, Measurements, Recurring [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total investments	27,502	15,735
Commercial paper [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total investments	27,502	15,735
Commercial paper [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total investments
Corporate bonds [Member] | Fair Value, Measurements, Recurring [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total investments	33,772	54,342
Corporate bonds [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total investments	33,772	54,342
Corporate bonds [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Summary of assets and liabilities measured at fair value on a recurring basis
Total investments