Notes Payable and Unsecured Credit Facilities Narrative (Details) ratio in Millions, $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($)	Mar. 09, 2018 USD ($)
Debt Instrument [Line Items]
Repayments of Lines of Credit	$ 60.0
Senior Notes [Member] \| Notes Due March 2028 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 300.0
Debt Instrument, Interest Rate, Stated Percentage		0.00%
Debt Instrument, Discount Percent		0.0
Notes Payable to Banks [Member] \| 150M 6% Notes [Member]
Debt Instrument [Line Items]
Repayments of Unsecured Debt	163.2
Accordion Feature [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Increase in Capacity	1,250.0
Mortgage Loan Maturities [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Year Two	$ 135.8

Debt Instrument, Discount Percent

No definition available.

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- Definition

Long term debt, maturities, repayments of principal, remainder of fiscal year and year two

+ References

No definition available.

+ Details

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

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-SubTopic 30
-Section 45
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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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- 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.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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

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- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
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-Paragraph 15
-Subparagraph (b)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

The cash outflow to repay long-term debt that is not secured by collateral. Excludes repayments of tax exempt unsecured debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6513228

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