Cash, Cash Equivalents and Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	$ 23,560	$ 46,186
Fair value of available-for-sale securities, continuous loss position for twelve month or longer	11,028	17,477
Total fair value of available-for-sale securities, continuous loss position	34,588	63,663
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(45)	(392)
Available-for-sale securities, continuous loss position for 12 months or greater, gross unrealized losses	(1,497)	(1,748)
Available-for-sale securities, total gross unrealized losses	(1,542)	(2,140)
Cost
Due in one year or less, Cost	109,030
Due after one year through ten years, Cost	87,528
Due after ten years, Cost	20,055
Total Cost	216,613
Fair Value
Due in one year or less, Fair Value	109,112
Due after one year through ten years, Fair Value	87,663
Due after ten years, Fair Value	18,558
Total Fair Value	215,333
Corporate bonds
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	13,019	25,438
Total fair value of available-for-sale securities, continuous loss position	13,019	25,438
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(36)	(363)
Available-for-sale securities, total gross unrealized losses	(36)	(363)
Auction rate securities
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for twelve month or longer	11,028	17,477
Total fair value of available-for-sale securities, continuous loss position	11,028	17,477
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for 12 months or greater, gross unrealized losses	(1,497)	(1,748)
Available-for-sale securities, total gross unrealized losses	(1,497)	(1,748)
Municipal bonds
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	8,431	10,437
Total fair value of available-for-sale securities, continuous loss position	8,431	10,437
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(8)	(12)
Available-for-sale securities, total gross unrealized losses	(8)	(12)
U.S. government agency
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months		5,772
Total fair value of available-for-sale securities, continuous loss position		5,772
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses		(12)
Available-for-sale securities, total gross unrealized losses		(12)
International government bonds
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	2,110
Total fair value of available-for-sale securities, continuous loss position	2,110
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(1)
Available-for-sale securities, total gross unrealized losses	(1)
Asset-backed securities
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months		4,539
Total fair value of available-for-sale securities, continuous loss position		4,539
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses		(5)
Available-for-sale securities, total gross unrealized losses		$ (5)