Investments and Fair Value Disclosures (Details) (USD $) In Thousands, unless otherwise specified					6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2012 Money market funds [Member]	Jun. 30, 2012 U.S. agency notes [Member]	Jun. 30, 2012 Commercial paper [Member]	Jun. 30, 2012 Corporate bonds [Member]
Summary of long-term investments
Total cash equivalents, Carrying Value	$ 84,253	$ 94,072	$ 157,984	$ 47,254	$ 53,160
Total short-term investments, Carrying Value	89,568	92,749				30,708	27,502	31,358
Total long-term investments, Carrying Value	$ 20,405	$ 5,000				$ 17,991		$ 2,414
Contracted maturity of cash and cash equivalents					demand
Contracted maturity of short term investments						30 – 382 days	9 - 258 days	32 – 349 days
Contracted maturity of long term investments						368 - 514 days		401 days