Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair value measurements of Company's financial assets and liabilities
Total assets	$ 127,522	$ 95,345
Total liabilities		10,472
Money market fund [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets	18,088	41,266
Government-sponsored agencies [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets	6,007	9,044
Commercial paper [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets	32,132	12,541
Corporate debt securities [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets	71,295	32,494
Convertible debt from related party [Member]
Fair value measurements of Company's financial assets and liabilities
Total liabilities		10,472
Level 1 [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets	18,088	41,266
Total liabilities
Level 1 [Member] | Money market fund [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets	18,088	41,266
Level 1 [Member] | Government-sponsored agencies [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets
Level 1 [Member] | Commercial paper [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets
Level 1 [Member] | Corporate debt securities [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets
Level 1 [Member] | Convertible debt from related party [Member]
Fair value measurements of Company's financial assets and liabilities
Total liabilities
Level 2 [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets	109,434	54,079
Total liabilities
Level 2 [Member] | Money market fund [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets
Level 2 [Member] | Government-sponsored agencies [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets	6,007	9,044
Level 2 [Member] | Commercial paper [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets	32,132	12,541
Level 2 [Member] | Corporate debt securities [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets	71,295	32,494
Level 2 [Member] | Convertible debt from related party [Member]
Fair value measurements of Company's financial assets and liabilities
Total liabilities
Level 3 [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets
Total liabilities		10,472
Level 3 [Member] | Money market fund [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets
Level 3 [Member] | Government-sponsored agencies [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets
Level 3 [Member] | Commercial paper [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets
Level 3 [Member] | Corporate debt securities [Member]
Fair value measurements of Company's financial assets and liabilities
Total assets
Level 3 [Member] | Convertible debt from related party [Member]
Fair value measurements of Company's financial assets and liabilities
Total liabilities		$ 10,472