Investments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Summary Of Short- and Long-term Investments
Available-for-sale securities, Amortized Cost	$ 180,403	$ 168,332
Available-for-sale securities, Gross Unrealized Gains	396	449
Available-for-sale securities, Gross Unrealized Losses	(49)	(2,551)
Available-for-sale securities, Estimated Fair Value	180,750	166,230
Short-term investments
Summary Of Short- and Long-term Investments
Available-for-sale securities, Amortized Cost		148,432
Available-for-sale securities, Gross Unrealized Gains		449
Available-for-sale securities, Gross Unrealized Losses		(178)
Available-for-sale securities, Estimated Fair Value		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	52,332	74,687
Available-for-sale securities due in one to three years, Amortized Cost	59,176	19,950
Available-for-sale securities due in one year or less, Gross Unrealized Gains	88	81
Available-for-sale securities due in one to three years, Gross Unrealized Gains	137	73
Available-for-sale securities due in one year or less, Gross Unrealized Losses	(6)	(115)
Available-for-sale securities due in one to three years, Gross Unrealized Losses	(37)	(50)
Available-for-sale securities due in one year or less, Estimated Fair Value	52,414	74,653
Available-for-sale securities due in one to three years, Estimated Fair Value	59,276	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	24,795	26,770
Available-for-sale securities due in one to three years, Amortized Cost	34,606	21,028
Available-for-sale securities due in one year or less, Gross Unrealized Gains	86	67
Available-for-sale securities due in one to three years, Gross Unrealized Gains	84	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	(2)
Available-for-sale securities due in one year or less, Estimated Fair Value	24,881	26,830
Available-for-sale securities due in one to three years, Estimated Fair Value	34,688	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	9,494	5,997
Available-for-sale securities due in one year or less, Gross Unrealized Gains	1
Available-for-sale securities due in one year or less, Gross Unrealized Losses	(4)	(6)
Available-for-sale securities due in one year or less, Estimated Fair Value	9,491	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