Derivatives and Hedging Activities - Additional Information (Detail)	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($) Derivative	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Derivative	Jun. 30, 2017 USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Termination value of derivatives in net liability position	$ 154,000		$ 154,000
Collateral posted for derivative instruments	1,000,000		1,000,000
Derivatives Designated as Hedging Instruments [Member] \| Cash Flow Hedging [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Effective portion of change in fair value of cash flow hedges	910,000	$ (1,157,000)	$ 3,112,000	$ (911,000)
Interest rate hedging exposure to variability in future cash flows for forecasted transactions, maximum period			18 years 2 months 19 days
Interest Rate Swap [Member] \| Derivatives Designated as Hedging Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) related to changes in fair value of swaps	4,000	2,000	$ 4,000	2,000
Interest Rate Swap [Member] \| Derivatives Designated as Hedging Instruments [Member] \| Fair Value Hedging [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of interest rate swaps	$ 5,700,000		$ 5,700,000
Number of interest rate swaps \| Derivative	1		1
Gain (Loss) related to changes in fair value of swaps	$ (49,000)	88,000	$ (130,000)	134,000
Interest Rate Swap [Member] \| Derivatives Designated as Hedging Instruments [Member] \| Cash Flow Hedging [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of interest rate swaps	$ 51,500,000		$ 51,500,000
Number of interest rate swaps \| Derivative	2		2
Effective portion of change in fair value of cash flow hedges	$ 910,000	(1,157,000)	$ 3,112,000	(911,000)
Reclassification from AOCI to interest expenses	7,000		7,000
Interest Rate Swap [Member] \| Derivatives not Designated as Hedging Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of interest rate swaps	$ 1,100,000,000		$ 1,100,000,000
Number of interest rate swaps \| Derivative	96		96
Gain (Loss) related to changes in fair value of swaps	$ 137,000	$ (168,000)	$ 473,000	$ (516,000)

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

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The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

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Maximum period the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of interest rate derivative instruments held by the entity at the reporting date.

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Amount, before tax and reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.

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