Fair Value Measurements (Details 3) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Available-for-sale marketable securities by rolling maturity, amortized cost
Due in one year or less	$ 55,573
Due in more than one year but less than five years	1,290
Total	56,863	67,635
Available-for-sale marketable securities by fiscal year maturity, amortized cost
Due in one year or less		67,635
Total	56,863	67,635
Available-for-sale marketable securities by rolling maturity, estimated fair value
Due in one year or less	55,570
Due in more than one year but less than five years	1,291
Total	56,861	67,605
Available-for-sale marketable securities by fiscal year maturity, estimated fair value
Due in one year or less		67,605
Total	$ 56,861	$ 67,605