Derivative Instruments (Schedule of Notional Amounts of Outstanding Derivative Positions) (Details) - Unsecured Debt	Dec. 31, 2018 USD ($) contract
Derivative [Line Items]
Derivative, notional amount	$ 450,000,000
Amended and Restated $300 Million Unsecured 2011 Term Loan \| Interest Rate Swap 1 through 3
Derivative [Line Items]
Number of swap agreements \| contract	3
Derivative, notional amount	$ 300,000,000
$250 Million Unsecured 2018 Term Loan
Derivative [Line Items]
Derivative, notional amount	$ 150,000,000
$250 Million Unsecured 2018 Term Loan \| Interest Rate Swap 4 through 5
Derivative [Line Items]
Number of swap agreements \| contract	2
Derivative, notional amount	$ 100,000,000
$250 Million Unsecured 2018 Term Loan \| Interest Rate Swap 6
Derivative [Line Items]
Number of swap agreements \| contract	1
Derivative, notional amount	$ 50,000,000

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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+ References

No definition available.

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

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