Derivative Instruments (Details) - Summary of financial operations derivatives credit exposure (USD $) In Thousands, unless otherwise specified			12 Months Ended			9 Months Ended
	Sep. 30, 2012	Dec. 31, 2010	Dec. 31, 2011 Credit Exposure [Member] Standard Poors BB Rating Member	Sep. 30, 2012 Credit Exposure [Member] Standard Poors BB Rating Member contracts	Sep. 30, 2012 Credit Exposure [Member] Standard Poors BB Rating Member Structured Finance [Member] contracts	Sep. 30, 2012 Credit Exposure [Member] Standard Poors BB Rating Member Project Finance Loan Participation [Member] contracts	Sep. 30, 2012 Credit Exposure [Member] Standard Poors BBB Minus Rating
Credit Derivatives [Line Items]
Principal outstanding			$ 78,425				$ 55,484
Interest outstanding			3,253				2,665
Aggregate outstanding exposure			81,678				58,149
Total liability recorded	$ 10,152	$ 15,763	$ 10,288				$ 3,626
Weighted average years to maturity			5 years				4 years 6 months 0 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%