Derivative Instruments - Summary of financial operations derivatives credit exposure (Details) (Credit exposure, Standard & Poor's, CC Rating, USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014 Contracts	Dec. 31, 2013
Credit exposure | Standard & Poor's, CC Rating
Credit Derivatives [Line Items]
Derivative Liability, Number of Instruments Held	1
Principal outstanding	$ 39,748	$ 42,080
Interest outstanding	1,598	2,154
Aggregate outstanding exposure	41,346	44,234
Total liability recorded	$ 8,930	$ 4,190
Weighted average contractual term to maturity	3 years 3 months 18 days	3 years 8 months 12 days
Project Finance Loan Participation Deficiency Guarantee Percentage	68.00%