Derivative Instruments (Details) - Summary of financial operations derivatives credit exposure (USD $)			12 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2010	Dec. 31, 2011 Credit Exposure [Member] Standard Poors BB Rating Member	Jun. 30, 2012 Credit Exposure [Member] Standard Poors BB Rating Member contracts	Jun. 30, 2012 Credit Exposure [Member] Standard Poors BB Rating Member Structured Finance [Member] contracts	Jun. 30, 2012 Credit Exposure [Member] Standard Poors BB Rating Member Project Finance Loan Participation [Member] contracts	Jun. 30, 2012 Credit Exposure [Member] Standard Poors BBB Minus Rating
Credit Derivatives [Line Items]
Principal outstanding			$ 78,425,000				$ 56,052,000
Interest outstanding			3,253,000				2,616,000
Aggregate outstanding exposure			81,678,000				58,668,000
Total liability recorded	10,152,000	15,763,000	10,288,000				3,626,000
Weighted average years to maturity			5 years				4 years 9 months 18 days
Number of derivatives held and other disclosures:
Number of instruments held				2	1	1
Deficiency guarantee from German state and federal governments (percentage)						80.00%
Reduction in exposure					$ 23,000,000