Derivatives and Hedging Activities - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Loss	$ 5,000	$ 25,000	$ 8,000	$ 58,000
Accumulated Other Comprehensive Income (Loss), Net of Tax	(4,599,000)	(30,467,000)	(4,599,000)	(30,467,000)	(26,054,000)	(35,848,000)
Unrealized losses from the effective portion of derivative instruments	1,826,000	2,903,000	(10,096,000)	8,197,000
Credit Risk Derivatives, description of contingent features			Certain of our derivative contracts contain a provision where if we default on any of our indebtedness, including default where repayment of the indebtedness has not been accelerated by the lender, then we could also be declared in default on our derivative obligations. As of September 30, 2013, we had not breached the provisions of these agreements.  If we had breached these provisions, we could have been required to settle our obligations under the agreements at their termination value of $6.7 million.
Derivative contracts, collateral			Certain of our derivative contracts are credit enhanced by either FNMA or Freddie Mac.  These derivative contracts require that our credit enhancing party maintain credit ratings above a certain level.  If our credit support providers were downgraded below Baa1 by Moody’s or BBB+ by Standard & Poor’s, or S&P, we may be required to either post 100 percent collateral or settle the obligations at their termination value of $9.7 million as of September 30, 2013.  Both FNMA and Freddie Mac are currently rated Aaa by Moody’s and AA+ by S&P, and therefore, the provisions of this agreement have not been breached and no collateral has been posted related to these agreements as of September 30, 2013.
Credit Risk Related Contingent Features Termination Value	9,700,000		9,700,000
Reclassification adjustment for losses included in net income for the effective portion of derivative instruments	3,621,000	4,815,000	12,098,000	15,308,000
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest			(739,000)	(1,730,000)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent			21,455,000	5,381,000
Credit Default Option [Member]
Derivative [Line Items]
Credit Risk Related Contingent Features Termination Value	500,000		500,000
Other Credit Enhancements
Derivative [Line Items]
Credit Risk Related Contingent Features Termination Value	6,700,000		6,700,000
Interest rate contracts
Derivative [Line Items]
Unrealized losses from the effective portion of derivative instruments	1,826,000	2,903,000	(10,096,000)	8,197,000
Termination
Derivative [Line Items]
Fair Value of Credit Risk Derivatives	9,800,000		9,800,000
Interest Expense
Derivative [Line Items]
Change in Fair Value of Derivatives, Ineffective portion	1,000	7,000	26,000	40,000
Interest Expense | Cash Flow Hedging [Member] | Interest Rate Caps
Derivative [Line Items]
Change in fair value of interest rate derivatives included in AOCI and expected to be reclassified in the next 12 months			8,900,000
Interest Expense | Interest rate contracts
Derivative [Line Items]
Reclassification adjustment for losses included in net income for the effective portion of derivative instruments	3,621,000	4,815,000	12,098,000	15,308,000
net liability position [Member]
Derivative [Line Items]
Credit Risk Related Contingent Features Termination Value	10,200,000		10,200,000
Designated as Hedging Instrument [Member] | Interest Rate Caps
Derivative [Line Items]
Derivative, Number of Instruments Held	12		12
Notional Amount of Interest Rate Derivatives	224,600,000		224,600,000
Not Designated as Hedging Instrument [Member] | Interest Rate Caps
Derivative [Line Items]
Derivative, Number of Instruments Held	11		11
Notional Amount of Interest Rate Derivatives	$ 63,800,000		$ 63,800,000