Derivatives and other Hedging Instruments - Additional Information (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Estimated amount related to derivatives reclassified to interest expense during the next 12 months	$ 59,146
The weighted-average remaining term of swaps	19 months
Total fair market value of Futures Contracts	(132,972)	(25,585)
Maximum leverage ratio the Company can reach before it could be in default of one of its derivative obligations	1000.00%
Other Purchase Commitment
Derivative [Line Items]
Derivatives	3,755	(658)
Eurodollar Future
Derivative [Line Items]
Notional Amount	1,000
Fair value of derivatives in net liability position, which includes accrued interest but excludes any adjustment for nonperformance risk, related to agreements	$ 77,583