Cash, Cash Equivalents, and Investments - Restricted Cash (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Restricted Cash and Investments [Abstract]
Restricted cash and investments	$ 102,661,000	$ 78,307,000
Restricted Cash [Member]
Restricted Cash and Investments [Abstract]
Restricted cash	900,000	600,000
Demand Deposits [Member]
Restricted Cash and Investments [Abstract]
Restricted cash	900,000	600,000
Restricted Investments [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	101,800,000	77,700,000
Corporate Debt Securities [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	1,900,000	1,600,000
Mutual Funds [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	1,200,000	1,000,000
Money Market Funds [Member]
Restricted Cash and Investments [Abstract]
Restricted investments	$ 98,700,000	$ 75,100,000