Concentration of Risks and Uncertainties (Details) (USD $)	Sep. 30, 2014
Concentration Risk [Line Items]
U.S. treasury securities	$ 484,900,000
Corporate debt securities	582,290,000
Preferred stock	13,724,000
Single Corporate Issuer
Concentration Risk [Line Items]
Corporate debt securities	$ 97,400,000

Amount of debt securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Name Accounting Standards Codification

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