Cash, Cash Equivalents, and Investments - Restricted Cash (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Restricted Cash and Investments [Abstract]
Restricted cash and investments	$ 78,307,000	$ 119,346,000
Restricted Cash [Member]
Restricted Cash and Investments [Abstract]
Restricted cash	600,000	1,700,000
Demand Deposits [Member]
Restricted Cash and Investments [Abstract]
Restricted cash	600,000	1,700,000
Restricted Investments [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	77,700,000	117,600,000
US Government Debt Securities [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	0	600,000
Corporate Debt Securities [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	1,600,000	2,700,000
Mutual Funds [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	1,000,000	0
Money Market Funds [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	$ 75,100,000	$ 114,300,000