Derivatives and Hedging Activities - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) Contract	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Contract	Sep. 30, 2014 USD ($)
Credit Default Option [Member]
Derivative [Line Items]
Credit Risk Related Contingent Features Termination Value	$ 18,900,000		$ 18,900,000
Termination
Derivative [Line Items]
Fair Value of Credit Risk Derivatives	18,000,000		18,000,000
Net Liability Position [Member]
Derivative [Line Items]
Credit Risk Related Contingent Features Termination Value	$ 18,900,000		$ 18,900,000
Interest Rate Forward Swap [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held | Contract	3		3
Derivative, Notional Amount	$ 150,000,000		$ 150,000,000
Designated as Hedging Instrument [Member] | Interest Rate Caps
Derivative [Line Items]
Derivative, Number of Instruments Held | Contract	5		5
Derivative, Notional Amount	$ 125,000,000		$ 125,000,000
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held | Contract	7		7
Derivative, Notional Amount	$ 550,000,000		$ 550,000,000
Designated as Hedging Instrument [Member] | Interest Expense
Derivative [Line Items]
Loss on Cash Flow Hedge Ineffectiveness	$ (44,000)	$ (25,000)	(117,000)	$ (88,000)
Change in fair value of interest rate derivatives included in AOCI and expected to be reclassified in the next 12 months			$ 5,000,000