Significant Accounting Policies (Detail) (USD $)	Sep. 30, 2011	Dec. 31, 2010	Dec. 31, 2010 Structured Project Loan [Member]	Sep. 30, 2010 Structured Project Loan [Member]	Sep. 30, 2011 Reinsurance Segment [Member]	Dec. 31, 2010 Reinsurance Segment [Member]
Valuation Allowances and Reserves, Balance			$ 9,900,000	$ 9,200,000	$ 108,200,000	$ 121,900,000
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net	42,100,000	42,300,000
Reinsurance Receivables					$ 3,800,000,000