Derivatives and Hedging Activities - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) Contract	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) Contract	Jun. 30, 2014 USD ($)
Credit Default Option [Member]
Derivative [Line Items]
Credit Risk Related Contingent Features Termination Value	$ 13,600,000		$ 13,600,000
Termination
Derivative [Line Items]
Fair Value of Credit Risk Derivatives	13,100,000		13,100,000
Net Liability Position [Member]
Derivative [Line Items]
Credit Risk Related Contingent Features Termination Value	$ 13,600,000		$ 13,600,000
Designated as Hedging Instrument [Member] | Interest Rate Caps
Derivative [Line Items]
Derivative, Number of Instruments Held | Contract	6		6
Derivative, Notional Amount	$ 165,000,000		$ 165,000,000
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held | Contract	8		8
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	$ (12,000)	$ (59,000)	(73,000)	$ (63,000)
Change in fair value of interest rate derivatives included in AOCI and expected to be reclassified in the next 12 months			$ 4,700,000