Cash, Cash Equivalents, and Investments - Restricted Cash (Details) (USD $)	Mar. 31, 2012	Dec. 31, 2011
Restricted Cash and Investments [Abstract]
Restricted cash and investments	$ 82,504,000	$ 78,307,000
Restricted Cash [Member]
Restricted Cash and Investments [Abstract]
Restricted cash	600,000	600,000
Demand Deposits [Member]
Restricted Cash and Investments [Abstract]
Restricted cash	600,000	600,000
Restricted Investments [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	81,900,000	77,700,000
Corporate Debt Securities [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	1,700,000	1,600,000
Mutual Funds [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	1,000,000	1,000,000
Money Market Funds [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	$ 79,200,000	$ 75,100,000