Summary of Significant Accounting Policies (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income taxes
The ownership percentage for which the entity files a consolidated federal income tax return, low end of range	80.00%
Cash and Cash Equivalents
Maximum maturity period of short-term and highly liquid interest bearing investments at time of purchase	3 months
Excess capital and undistributed earnings included in cash and cash equivalents	$ 47,300,000
Restricted Assets
Restricted cash	226,554,000	185,794,000	116,734,000
Restricted short-term investments	88,332,000	129,599,000
Restricted deposits (included in other current assets)	20,846,000	20,453,000
Restricted long-term investments	32,563,000	7,956,000
Total	$ 368,295,000	$ 343,802,000