Fair Value Measures and Other Financial Instruments (Derivatives and other financial instruments) - Additional Information (Detail)	6 Months Ended
Jun. 30, 2016 USD ($) Agreement	Dec. 31, 2015 USD ($)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Accumulated comprehensive income (loss) to interest expense, future periods	$ 3,173,000
Termination payment	7,153,000
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Net liabilities	$ 7,077,000	$ 3,365,000
Unsecured Bank Term Loan [Member] \| Current Interest Rate Swap [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Number of interest rate swap agreements \| Agreement	4
Notional amounts	$ 300,000,000
Interest rate, effective	1.54%
Derivative maturity period	2018-01
Derivative, fixed interest rate	2.69%
Unsecured Bank Term Loan [Member] \| Future Interest Rate Swap [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Number of interest rate swap agreements \| Agreement	4
Notional amounts	$ 300,000,000
Interest rate, effective	1.37%
Derivative maturity period	2020-01
Derivative, fixed interest rate	2.52%
Unsecured Bank Term Loan [Member] \| Future Interest Rate Swap [Member] \| New Four Interest Rate Swap
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notional amounts	$ 300,000,000

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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- Definition

Derivative maturity.

+ References

No definition available.

+ Details

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- Definition

The blended rate at which the LIBOR component is effectively fixed for the company's term loan under its existing interest rate swap arrangement.

+ References

No definition available.

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- Definition

The aggregate fair value of assets needed to immediately settle the derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624258-113959

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- Definition

Fair value, after offset of derivative asset, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=d3e41678-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226006-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

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- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

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- Definition

The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings.

+ References

No definition available.

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- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5579245-113959

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- Definition

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.

+ References

No definition available.

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