Derivatives and other Hedging Instruments - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative [Line Items]
Effective hedge losses reclassified into earnings	$ 29,929,000	$ 27,811,000
Ineffective losses recorded on a current basis in earnings	(116,000)	(169,000)
Estimated amount related to derivatives reclassified to interest expense during the next 12 months	116,526,000
Future cash flows for forecasted transactions, average period in months	30 months
Gain recognized due to change in fair value of contracts	51,000
Futures contracts - Asset Derivatives found in Other Assets	51,000
Derivative, description of terms	The Company’s total Futures Contracts are designed to replicate interest rate swaps with a notional amount was $200.0 million at March 31, 2013. Our Futures Contracts had a weighted average swap equivalent rate of 1.04% and weighted average term of 42 months as of March 31, 2013.
Maximum leverage ratio the Company can reach before it could be in default of one of its derivative obligations	10 to 1
Fair value of derivatives in net liability position, which includes accrued interest but excludes any adjustment for nonperformance risk, related to agreements	220,040,000
Eurodollar Futures Contracts
Derivative [Line Items]
Future cash flows for forecasted transactions, average period in months	42 months
Futures contracts notional amount	$ 200,000,000
Weighted average swap equivalent rate	1.04%