Derivatives and other Hedging Instruments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013
Derivative [Line Items]
Estimated amount related to derivatives reclassified to interest expense during the next 12 months		$ 89,887
The weighted-average remaining term of swaps		27 months
Realized loss on futures contracts	(27,327)	(27,327)
Unrealized loss on futures contracts	(50,129)	(44,593)
Maximum leverage ratio the Company can reach before it could be in default of one of its derivative obligations		10 to 1
Eurodollar Futures Contracts
Derivative [Line Items]
The weighted-average remaining term of swaps		60 months
Derivative, description of terms	The Company's total futures contracts designed to replicate interest rate swaps had a notional equivalent amount of $4,700 at September 30, 2013 with a weighted average swap equivalent rate of 1.65% and a weighted average term of 60 months. As of September 30, 2013, the fair value of all futures contracts was a liability of $44,593.
Weighted average swap equivalent rate	1.65%	1.65%
Fair value of all futures contracts, liability	44,593	44,593
Realized loss on futures contracts	(27,327)	(27,327)
Unrealized loss on futures contracts	(50,129)	(44,593)
Fair value of derivatives in net liability position, which includes accrued interest but excludes any adjustment for nonperformance risk, related to agreements	134,328	134,328
Foreign exchange future | Eurodollar Futures Contracts
Derivative [Line Items]
Futures contracts notional amount	$ 4,700	$ 4,700