Derivative Instruments and Hedging Activities - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) Swap	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) Swap	Jun. 30, 2014 USD ($)	Jun. 10, 2015 USD ($)	Dec. 31, 2014 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Loss related to ineffective portion of derivatives recognized in other expense(income), net	$ 1,000	$ 0	$ 287,000	$ 0
Reclassified as an increase to interest expense, expected during the next 12 months	3,252,000		3,252,000
Tax benefit on unrealized loss on derivatives			(2,892,000)
Termination value of derivatives in a net liability position	9,980,000		9,980,000
Collateral posted relating to credit risk-related contingent features	0		0
Forward Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of interest rate swap					$ 1,000,000,000
Combined Interest Rate Cash Flow Hedges, All Swaps [Member] | Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of interest rate swap	$ 1,250,000,000		$ 1,250,000,000
Number of outstanding interest rate derivatives | Swap	4		4
Combined Interest Rate Cash Flow Hedges, All Swaps [Member] | Forward Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of interest rate swap	$ 1,000,000,000		$ 1,000,000,000
Number of outstanding interest rate derivatives | Swap	5		5
Not Designated as Hedge Accounting Relationships [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives outstanding	$ 0		$ 0			$ 0