Commitments and Contingencies - Financial and other guarantee exposures(Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Guarantee_contracts	Dec. 31, 2013 Guarantee_contracts
Commitments and Contingencies Disclosure [Abstract]
Number of financial guarantee contracts at beginning of period	3	4
Number of financial guarantee contracts matured, prepaid or commuted during the period	(1)	(1)
Number of financial guarantee contracts at end of period	2	3
Principal outstanding	$ 80,813	$ 108,255
Interest outstanding	0	0
Aggregate exposure outstanding	80,813	108,255
Total gross claim liability recorded	0	0
Total unearned premiums and fees recorded	$ 0	$ 134
Weighted average contractual term to maturity in years	25 years 2 months 12 days	26 years 0 months 0 days