Schedule of Derivative Assets and Liabilities by Counterparty (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	$ 144,532
JP Morgan Chase [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	46,908
Morgan Stanley [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	17,411
Merrill Lynch [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	16,979
Barclays Capital [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	16,923
Den Norske Bank [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	8,928
Societe Generale [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	8,754
Macquarie Bank [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	8,146
J. Aron & Company [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	6,817
Wells Fargo Bank, N.A. [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	4,969
Citibank N [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	4,857
Deutsche Bank [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	1,374
BMO Financial Group [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	1,041
Credit Suisse [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	992
BP Corporation North America [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	793
Royal Bank of Canada [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	752
BNP Paribas [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	473
Toronto Dominion [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	(476)
Mitsubishi UFJ Financial Group [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	(504)
Credit Agricole [Member]
Schedule of Derivative Assets and Liabilities by Counterparty [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	$ (605)