Investments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Summary Of Short- and Long-term Investments
Available-for-sale securities, Amortized Cost	$ 176,343	$ 168,332
Available-for-sale securities, Gross Unrealized Gains	349	449
Available-for-sale securities, Gross Unrealized Losses	(121)	(2,551)
Available-for-sale securities, Estimated Fair Value	176,571	166,230
Short-term investments
Summary Of Short- and Long-term Investments
Available-for-sale securities, Amortized Cost	176,343	148,432
Available-for-sale securities, Gross Unrealized Gains	349	449
Available-for-sale securities, Gross Unrealized Losses	(121)	(178)
Available-for-sale securities, Estimated Fair Value	176,571	148,703
Short-term investments | Corporate debt securities
Summary Of Short- and Long-term Investments
Available-for-sale securities due in one year or less, Amortized Cost	57,598	74,687
Available-for-sale securities due in one to three years, Amortized Cost	52,577	19,950
Available-for-sale securities due in one year or less, Gross Unrealized Gains	86	81
Available-for-sale securities due in one to three years, Gross Unrealized Gains	64	73
Available-for-sale securities due in one year or less, Gross Unrealized Losses	(37)	(115)
Available-for-sale securities due in one to three years, Gross Unrealized Losses	(70)	(50)
Available-for-sale securities due in one year or less, Estimated Fair Value	57,647	74,653
Available-for-sale securities due in one to three years, Estimated Fair Value	52,571	19,973
Short-term investments | U.S. treasury and government agency securities
Summary Of Short- and Long-term Investments
Available-for-sale securities due in one year or less, Amortized Cost	17,972	26,770
Available-for-sale securities due in one to three years, Amortized Cost	40,709	21,028
Available-for-sale securities due in one year or less, Gross Unrealized Gains	95	67
Available-for-sale securities due in one to three years, Gross Unrealized Gains	104	228
Available-for-sale securities due in one year or less, Gross Unrealized Losses		(7)
Available-for-sale securities due in one to three years, Gross Unrealized Losses	(4)
Available-for-sale securities due in one year or less, Estimated Fair Value	18,067	26,830
Available-for-sale securities due in one to three years, Estimated Fair Value	40,809	21,256
Short-term investments | Commercial paper
Summary Of Short- and Long-term Investments
Available-for-sale securities due in one year or less, Amortized Cost	7,487	5,997
Available-for-sale securities due in one year or less, Gross Unrealized Losses	(10)	(6)
Available-for-sale securities due in one year or less, Estimated Fair Value	7,477	5,991
Long-term investments
Summary Of Short- and Long-term Investments
Available-for-sale securities, Amortized Cost		19,900
Available-for-sale securities, Gross Unrealized Losses		(2,373)
Available-for-sale securities, Estimated Fair Value		17,527
Long-term investments | Auction rate securities
Summary Of Short- and Long-term Investments
Available-for-sale securities due after five years, Amortized Cost		19,900
Available-for-sale securities due after five years, Gross Unrealized Losses		(2,373)
Available-for-sale securities due after five years, Estimated Fair Value		$ 17,527