Secured and Unsecured Debt of the Company (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Outstanding borrowings (1)	$ 1,847,351	$ 1,844,634
Secured debt, net	$ 472,772	380,835
Maximum dividend payment as percentage of funds from operations	95.00%
Line of credit [Member] \| $150.0 million term loan facility [Member]
Debt Instrument [Line Items]
Outstanding borrowings (1)	$ 150,000
Unsecured debt [Member]
Debt Instrument [Line Items]
Long-term debt	1,800,000	$ 1,800,000
Unsecured debt [Member] \| $39 million unsecured term loan due July 2019 [Member]
Debt Instrument [Line Items]
Outstanding borrowings (1)	$ 39,000
Unsecured senior notes [Member] \| 4.80% unsecured senior notes due July 15, 2018 [Member]
Debt Instrument [Line Items]
Stated interest rate	4.80%
Unsecured senior notes [Member] \| 6.625% unsecured senior notes due June 1, 2020 [Member]
Debt Instrument [Line Items]
Stated interest rate	6.625%
Unsecured senior notes [Member] \| 3.800% unsecured senior notes [Member]
Debt Instrument [Line Items]
Stated interest rate	3.80%
Unsecured senior notes [Member] \| 3.48% unsecured senior notes due October 1, 2025 [Member]
Debt Instrument [Line Items]
Stated interest rate	4.375%
Unsecured senior notes [Member] \| 4.25% unsecured senior notes [Member]
Debt Instrument [Line Items]
Stated interest rate	4.25%

Maximum dividend payment threshold amount as percentage of funds from operations per line of credit covenant.

No definition available.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ 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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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.

+ References

No definition available.

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ 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(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
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-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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