Fair Value Measurements (Details 1)	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Corporate obligations [Member]
Summary of weighted averages includes in significant inputs for the interest only strips valuation
Coupon rate	0.35%	0.60%
Maturity	21 years 10 months 21 days	21 years 5 months 9 days
Yield	0.68%	7.20%
U.S. agency obligations [Member]
Summary of weighted averages includes in significant inputs for the interest only strips valuation
Coupon rate	0.00%	6.91%
Maturity	0 years	1 year 3 months 29 days
Yield	0.00%	2.13%
Collateralized debt obligations [Member]
Summary of weighted averages includes in significant inputs for the interest only strips valuation
Coupon rate	1.13%	0.86%
Maturity	1 year 5 months 9 days	1 year 6 months 18 days
Yield	10.39%	11.79%
Other asset-backed securities [Member]
Summary of weighted averages includes in significant inputs for the interest only strips valuation
Coupon rate	0.87%	1.41%
Maturity	8 years 2 months 5 days	3 years
Yield	7.50%	4.50%
European ABS transactions [Member]
Summary of weighted averages includes in significant inputs for the interest only strips valuation
Coupon rate	1.59%	1.56%
Maturity	9 years 9 months 7 days	11 years 11 months 27 days
Yield	4.04%	3.90%