Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013 Guarantee_contracts	Dec. 31, 2012 Guarantee_contracts
Guarantor Obligations [Line Items]
Opening number of financial guarantee contracts	4	4
Number of financial guarantee contracts matured, prepaid or commuted during the period	0	0
Closing number of financial guarantee contracts	4	4
Principal outstanding	$ 115,464	$ 115,464
Interest outstanding	0	0
Aggregate exposure outstanding	115,464	115,464
Total gross claim liability recorded	1,399	1,399
Total unearned premiums and fees recorded	243	279
Weighted average term to maturity	25 years 2 months 12 days	25 years 4 months 24 days
Financial Guarantee Related to Future Scheduled Repayments On Government Subsidized Housing Project [Member]
Guarantor Obligations [Line Items]
Aggregate exposure outstanding	7,200
Financial Guarantee Related to Securities Including Some Issued By European Financials [Member]
Guarantor Obligations [Line Items]
Aggregate exposure outstanding	$ 108,300