Investments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Summary Of Short- and Long-term Investments
Available-for-sale securities, Amortized Cost	$ 182,537	$ 180,403
Available-for-sale securities, Gross Unrealized Gains	237	396
Available-for-sale securities, Gross Unrealized Losses	(179)	(49)
Available-for-sale securities, Estimated Fair Value	182,595	180,750
Corporate debt securities
Summary Of Short- and Long-term Investments
Available-for-sale securities due in one year or less, Amortized Cost	45,645	52,332
Available-for-sale securities due in one to three years, Amortized Cost	84,020	59,176
Available-for-sale securities due in one year or less, Gross Unrealized Gains	67	88
Available-for-sale securities due in one to three years, Gross Unrealized Gains	92	137
Available-for-sale securities due in one year or less, Gross Unrealized Losses	(2)	(6)
Available-for-sale securities due in one to three years, Gross Unrealized Losses	(158)	(37)
Available-for-sale securities due in one year or less, Estimated Fair Value	45,710	52,414
Available-for-sale securities due in one to three years, Estimated Fair Value	83,954	59,276
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	22,551	24,795
Available-for-sale securities due in one to three years, Amortized Cost	30,321	34,606
Available-for-sale securities due in one year or less, Gross Unrealized Gains	25	86
Available-for-sale securities due in one to three years, Gross Unrealized Gains	53	84
Available-for-sale securities due in one to three years, Gross Unrealized Losses	(19)	(2)
Available-for-sale securities due in one year or less, Estimated Fair Value	22,576	24,881
Available-for-sale securities due in one to three years, Estimated Fair Value	30,355	34,688
Commercial paper
Summary Of Short- and Long-term Investments
Available-for-sale securities due in one year or less, Amortized Cost		9,494
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)
Available-for-sale securities due in one year or less, Estimated Fair Value		$ 9,491