Indebtedness - Information Regarding Indebtedness (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Mortgage Loans Payable, Net	$ 631,880	$ 656,329
Unamortized Premiums	(141)	(161)
Mortgage Loans Payable, Gross	631,739	656,168
Senior Unsecured Notes, Net	445,925	474,150
Unamortized Discounts	1,776	2,570
Senior Unsecured Notes, Gross	447,701	476,720
Unsecured Credit Facility	108,000	98,000
Secured Debt
Debt Instrument [Line Items]
Interest Rate, Minimum	4.03%
Interest Rate, Maximum	8.26%
Effective Interest Rate, Minimum	4.03%
Effective Interest Rate, Maximum	8.26%
Maturity Date Range, Start	Jan. 01, 2014
Maturity Date Range, End	Sep. 01, 2022
2016 Notes
Debt Instrument [Line Items]
Senior Unsecured Notes, Net	159,538	159,510
Interest Rate	5.75%
Effective Interest Rate	5.91%
Maturity Date	Jan. 15, 2016
2017 Notes
Debt Instrument [Line Items]
Senior Unsecured Notes, Net	55,388	55,385
Interest Rate	7.50%
Effective Interest Rate	7.52%
Maturity Date	Dec. 01, 2017
2027 Notes
Debt Instrument [Line Items]
Senior Unsecured Notes, Net	6,066	6,066
Interest Rate	7.15%
Effective Interest Rate	7.11%
Maturity Date	May 15, 2027
2028 Notes
Debt Instrument [Line Items]
Senior Unsecured Notes, Net	32,257	55,261
Interest Rate	7.60%
Effective Interest Rate	8.13%
Maturity Date	Jul. 15, 2028
2032 Notes
Debt Instrument [Line Items]
Senior Unsecured Notes, Net	10,511	11,500
Interest Rate	7.75%
Effective Interest Rate	7.87%
Maturity Date	Apr. 15, 2032
2014 Notes
Debt Instrument [Line Items]
Senior Unsecured Notes, Net	80,401	79,683
Interest Rate	6.42%
Effective Interest Rate	6.54%
Maturity Date	Jun. 01, 2014
2017 II Notes
Debt Instrument [Line Items]
Senior Unsecured Notes, Net	$ 101,764	$ 106,745
Interest Rate	5.95%
Effective Interest Rate	6.37%
Maturity Date	May 15, 2017
Line of Credit
Debt Instrument [Line Items]
Interest Rate	1.893%
Effective Interest Rate	1.893%
Maturity Date	Dec. 12, 2014

Secured debt gross.

No definition available.

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- Definition

Unsecured debt gross.

+ References

No definition available.

+ Details

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Definition

When presenting a range of interest rates, the highest effective rate for funds borrowed under the debt agreement as of the balance sheet date.

+ References

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- Definition

When presenting a range of interest rates, the lowest effective rate for funds borrowed under the debt agreement as of the balance sheet date.

+ References

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- Definition

Interest rate stated in the contractual debt agreement.

+ References

+ Details

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- Definition

When presenting a range of interest rates, the highest stated (contractual) rate for funds borrowed under the debt agreement as of the balance sheet date.

+ References

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- Definition

When presenting a range of interest rates, the lowest stated (contractual) rate for funds borrowed under the debt agreement as of the balance sheet date.

+ References

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- Details

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(2))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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- Definition

Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

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- Definition

Earliest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

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- Definition

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 1A

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

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-Publisher FASB

-Name FASB Staff Position (FSP)

-Number APB14-1

-Paragraph 31

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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- Definition

The amount of debt premium that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

+ Details

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

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-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

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- Definition

The effective interest rate at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

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-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

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- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

+ Details

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- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

+ Details

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