Commitments and Contingencies (Details) - Financial and other guarantee exposures (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012 contracts	Dec. 31, 2011 contracts
Financial Guarantee Member
Guarantor Obligations [Line Items]
Number of financial guarantee contracts at beginning of period	4	37
Number of financial guarantee contracts matured, prepaid or commuted during the period	0	(33)
Number of financial guarantee contracts at end of period	4	4
Principal outstanding	$ 115,464	$ 115,464
Interest outstanding	0	0
Aggregate outstanding exposure	115,464	115,464
Total gross claim liability recorded	1,399	1,399
Total unearned premiums and fees recorded	316	425
Weighted average contractual term to maturity	25 years 8 months 12 days	26 years 8 months 12 days
Financial Guarantee Related to Securities Including Some Issued By European Financials [Member]
Guarantor Obligations [Line Items]
Number of financial guarantee contracts at end of period	3
Aggregate outstanding exposure	108,300
Financial Guarantee Related to Future Scheduled Repayments On Government Subsidized Housing Project [Member]
Guarantor Obligations [Line Items]
Aggregate outstanding exposure	$ 7,200