Marketable Securities and Time Deposits (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Summary of available-for-sale securities and short-term deposits
Amortized cost	$ 89,734	$ 100,701
Unrealized gains (losses), net	(109)	(1,029)
Estimated fair value	89,625	99,672
Short -term deposits [Member]
Summary of available-for-sale securities and short-term deposits
Amortized cost	2,615	15,803
Unrealized gains (losses), net
Estimated fair value	2,615	15,803
U.S. GSE securities [Member]
Summary of available-for-sale securities and short-term deposits
Amortized cost	3,763	10,725
Unrealized gains (losses), net	2	(29)
Estimated fair value	3,765	10,696
Corporate obligations [Member]
Summary of available-for-sale securities and short-term deposits
Amortized cost	83,356	74,173
Unrealized gains (losses), net	(111)	(1,000)
Estimated fair value	$ 83,245	$ 73,173