Summary of Significant Accounting Policies (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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	$ 65,500,000
Restricted Assets
Restricted cash	215,325,000	236,696,000	226,554,000
Restricted short-term investments	132,808,000	117,674,000
Restricted deposits (included in other current assets)	30,620,000	25,009,000
Restricted long-term investments	43,293,000	32,430,000
Total	$ 422,046,000	$ 411,809,000