Fair Value Measurements (Details 3) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Available-for-sale marketable securities by rolling maturity, amortized cost
Due in one year or less	$ 68,236
Due in more than one year but less than five years	770
Total	69,006	67,635
Available-for-sale marketable securities by fiscal year maturity, amortized cost
Due in one year or less		67,635
Total	69,006	67,635
Available-for-sale marketable securities by rolling maturity, estimated fair value
Due in one year or less	68,251
Due in more than one year but less than five years	771
Total	69,022	67,605
Available-for-sale marketable securities by fiscal year maturity, estimated fair value
Due in one year or less		67,605
Total	$ 69,022	$ 67,605