Commitments and Contingencies (Details) - Financial and other guarantee exposures (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2012 contracts	Dec. 31, 2011 contracts
Financial Guarantee Member
Guarantor Obligations [Line Items]
Number of financial guarantee contracts at January 1	4	37
Number of financial guarantee contracts matured, prepaid or commuted during the period	0	(33)
Number of financial guarantee contracts at December 31	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	352	425
Weighted average contractual term to maturity	25 years 10 months 24 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 December 31	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