Derivative Instruments and Hedging Activities - Additional Information (Detail)	3 Months Ended	6 Months Ended
	Jun. 30, 2017 USD ($) Swap	Jun. 30, 2017 USD ($) Swap	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($) Swap
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness on cash flow hedges	$ 0	$ 0
Reclassified as an increase to interest expense, expected during the next 12 months	10,122,000	10,122,000
Termination value of derivatives in a net liability position	20,842,000	20,842,000
Collateral posted relating to credit risk-related contingent features	0	0
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 interest rate swaps held | Swap	5	5
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
Number of interest rate swaps matured | Swap				4
Combined Interest Rate Cash Flow Hedges, All Swaps [Member] | Forward Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of interest rate swap				$ 1,000,000,000
Number of interest rate swaps held | Swap				5
Not Designated as Hedge Accounting Relationships [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives outstanding	$ 0	$ 0	$ 0