Investments and Fair Value Measurement (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	$ 68,280	$ 73,288
Cash equivalents [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	10,397	18,836
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	57,883	54,452
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	10,397	15,839
U.S. government sponsored entity debt securities [Member] | Cash equivalents [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities		2,997
U.S. government sponsored entity debt 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	57,883	54,452
Level 1 [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	10,397	15,839
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	10,397	15,839
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
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	10,397	15,839
Level 1 [Member] | U.S. government sponsored entity debt 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]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities	57,883	57,449
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		2,997
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	57,883	54,452
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] | Cash equivalents [Member]
Summary of fair value measurements of cash equivalents and available-for-sale marketable securities
Total cash equivalents and marketable securities		2,997
Level 2 [Member] | U.S. government sponsored entity debt 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	57,883	54,452
Level 3 [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] | 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