Short -Term Investments (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Cost and fair value of our debt investments
Due in one year or less, Amortized Costs	$ 35,480	$ 49,667
Due within two years, Amortized Costs		3,322
Total, Amortized Costs	35,480	52,989
Due in one year or less, Fair Value	35,470	49,569
Due within two years, Fair Value		3,318
Total, Fair Value	$ 35,470	$ 52,887