Investments and Fair Value Measurement (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	$ 77,265	$ 82,624
Cash equivalents [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	15,021	15,258
Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	62,244	67,366
Money market funds [Member] | Cash equivalents [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	15,021	15,258
U.S. government sponsored entity debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	47,860	27,013
U.S. treasury debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities		752
Corporate debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	14,384	39,601
Level 1 [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	15,021	15,258
Level 1 [Member] | Cash equivalents [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	15,021	15,258
Level 1 [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 1 [Member] | Money market funds [Member] | Cash equivalents [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	15,021	15,258
Level 1 [Member] | U.S. government sponsored entity debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 1 [Member] | U.S. treasury debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 1 [Member] | Corporate debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 2 [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	62,244	67,366
Level 2 [Member] | Cash equivalents [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 2 [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	62,244	67,366
Level 2 [Member] | Money market funds [Member] | Cash equivalents [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 2 [Member] | U.S. government sponsored entity debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	47,860	27,013
Level 2 [Member] | U.S. treasury debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities		752
Level 2 [Member] | Corporate debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	14,384	39,601
Level 3 [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 3 [Member] | Cash equivalents [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 3 [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 3 [Member] | Money market funds [Member] | Cash equivalents [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 3 [Member] | U.S. government sponsored entity debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 3 [Member] | U.S. treasury debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities
Level 3 [Member] | Corporate debt securities [Member] | Marketable securities [Member] | Available-for-sale securities [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities