Secured Debt and Unsecured Debt (Details) $ in Thousands	12 Months Ended
Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Unamortized discount	$ 10,000	$ 6,700
Weighted Average Interest Rate	3.74%
Weighted Average Years to Maturity	5 years 10 days
Deferred Finance Costs, Net		0
Borrowings outstanding	$ 2,300	1,900
Total Unsecured Debt	2,193,850	2,210,978
Total Debt	3,570,795	3,565,299
Fixed Rate Debt
Debt Instrument [Line Items]
Principal outstanding	$ 952,801	963,713
Weighted Average Interest Rate	4.93%
Weighted Average Years to Maturity	3 years 8 months 19 days
Number of Communities Encumbered	26
Variable Rate Debt
Debt Instrument [Line Items]
Principal outstanding	$ 424,144	390,608
Weighted Average Interest Rate	1.53%
Weighted Average Years to Maturity	4 years 6 months 10 days
Number of Communities Encumbered	11
Unsecured Revolving Credit Facility due October Two Thousand Fifteen [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	1.19%
Weighted Average Years to Maturity	4 years 30 days
Borrowings outstanding	$ 150,000	152,500
Tax Exempt Notes Payable [Member] \| Variable Rate Debt
Debt Instrument [Line Items]
Weighted Average Interest Rate	0.75%
Weighted Average Years to Maturity	7 years 2 months 8 days
Number of Communities Encumbered	2
Line of Credit [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.23%
Weighted Average Years to Maturity	3 years 20 days
Number of Communities Encumbered	18
Line of Credit [Member] \| Variable Rate Debt
Debt Instrument [Line Items]
Debt Instrument, Interest Rate at Period End	1.71%
Weighted Average Years to Maturity	4 years 19 days
Number of Communities Encumbered	8
Mortgages [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Weighted Average Interest Rate	4.57%
Weighted Average Years to Maturity	4 years 6 months 3 days
Number of Communities Encumbered	8
Mortgages [Member] \| Variable Rate Debt
Debt Instrument [Line Items]
Weighted Average Interest Rate	2.19%
Weighted Average Years to Maturity	1 year 26 days
Number of Communities Encumbered	1
Five Point Two Five Percent, Medium Term Notes, Due January 2015 [Member]
Debt Instrument [Line Items]
Unamortized discount	$ 0	6
Weighted Average Interest Rate	0.00%
Weighted Average Years to Maturity	0 years
Senior Unsecured Notes	$ 0	325,169
Four Point Two Five Percentage Medium-Term Notes due June 2018 [Member]
Debt Instrument [Line Items]
Unamortized discount	$ 1,037	1,465
Weighted Average Interest Rate	4.25%
Weighted Average Years to Maturity	2 years 5 months 1 day
Senior Unsecured Notes	$ 298,963	298,535
ThreePointSevenTermNotesDueOctober2020 [Member]
Debt Instrument [Line Items]
Weighted Average Years to Maturity	4 years 9 months 1 day
Senior Unsecured Notes	$ 299,962	299,954
1.44% Term notes due January 2021 [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	1.44%
Weighted Average Years to Maturity	5 years 29 days
Senior Unsecured Notes	$ 315,000	315,000
Three point seven percent medium term note due October 2020 [Member]
Debt Instrument [Line Items]
Unamortized discount	$ 38	46
Weighted Average Interest Rate	3.70%
Secured Debt [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 1,376,945	1,354,321
Weighted Average Interest Rate	3.88%
Weighted Average Years to Maturity	3 years 11 months 19 days
Number of Communities Encumbered	37
Total Debt	$ 1,376,945
Secured Debt [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Total Debt	952,801
Secured Debt [Member] \| Variable Rate Debt
Debt Instrument [Line Items]
Total Debt	$ 424,144
Unsecured Debt [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.64%
Weighted Average Years to Maturity	5 years 8 months 8 days
Total Unsecured Debt	$ 2,193,850	2,210,978
Total Debt	2,193,850
Four Point Six Three Percent Term Medium Notes Due January Two Thousand Twenty-Two [Member]
Debt Instrument [Line Items]
Unamortized discount	$ 2,164	2,523
Weighted Average Interest Rate	4.63%
Weighted Average Years to Maturity	6 years 10 days
Senior Unsecured Notes	$ 397,836	397,477
3.75 MTN Due July 2024 [Member]
Debt Instrument [Line Items]
Unamortized discount	$ 938	990
Weighted Average Interest Rate	3.75%
Weighted Average Years to Maturity	8 years 6 months 1 day
Senior Unsecured Notes	$ 299,114	299,010
Eight Point Five Zero Percent, Debentures, Due September 2024 [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	8.50%
Weighted Average Years to Maturity	8 years 8 months 15 days
Senior Unsecured Notes	$ 15,644	15,644
4.00% MTN Due October 2025 [Member]
Debt Instrument [Line Items]
Unamortized discount	$ 671	0
Weighted Average Interest Rate	4.00%
Weighted Average Years to Maturity	9 years 9 months 1 day
Senior Unsecured Notes	$ 299,329	0
Others [Member]
Debt Instrument [Line Items]
Senior Unsecured Notes	$ 24	27
Unsecured Working Capital Credit Facility due January 2019 [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	0.00%
Weighted Average Years to Maturity	3 years
Borrowings outstanding	$ 0	0
1.21% Term Loan Facility due January 2021 [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	1.21%
Weighted Average Years to Maturity	5 years 29 days
Senior Unsecured Notes	$ 35,000	35,000
Five Point Two Five Percent, Medium Term Notes, Due January 2016 [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	5.25%
Weighted Average Years to Maturity	15 days
Senior Unsecured Notes	$ 83,260	83,260
6.21 Medium Term Note, Due January 2016 [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	6.21%
Weighted Average Years to Maturity	6 months 5 days
Senior Unsecured Notes	$ 12,091	0
Reported Value Measurement [Member] \| Fair Value, Measurements, Recurring [Member] \| Tax Exempt Notes Payable [Member] \| Tax Exempt Notes Payable [Member] \| Variable Rate Debt
Debt Instrument [Line Items]
Principal outstanding	94,700	94,700
Reported Value Measurement [Member] \| Fair Value, Measurements, Recurring [Member] \| Line of Credit [Member] \| Line of Credit [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Principal outstanding	514,462	568,086
Reported Value Measurement [Member] \| Fair Value, Measurements, Recurring [Member] \| Line of Credit [Member] \| Line of Credit [Member] \| Variable Rate Debt
Debt Instrument [Line Items]
Principal outstanding	299,378	266,196
Reported Value Measurement [Member] \| Fair Value, Measurements, Recurring [Member] \| Mortgages [Member] \| Mortgages [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Principal outstanding	442,617	401,210
Reported Value Measurement [Member] \| Fair Value, Measurements, Recurring [Member] \| Mortgages [Member] \| Mortgages [Member] \| Variable Rate Debt
Debt Instrument [Line Items]
Principal outstanding	31,337	31,337
Unsecured Debt [Member]
Debt Instrument [Line Items]
Deferred Finance Costs, Net	(12,373)	(10,598)
Secured Debt [Member]
Debt Instrument [Line Items]
Deferred Finance Costs, Net		(7,208)
Secured Debt [Member] \| Variable Rate Debt
Debt Instrument [Line Items]
Deferred Finance Costs, Net	(1,271)	(1,625)
Secured Debt [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Deferred Finance Costs, Net	$ (4,278)	$ (5,583)

Debt instrument weighted average years to maturity.

No definition available.

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- Definition

Number of Communities Encumbered.

+ References

No definition available.

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- Definition

Secured debt including debt on real estate held for sale.

+ References

No definition available.

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Balance Type:	credit
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- Definition

The average effective interest rate during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
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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.

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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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- Definition

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

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

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- Definition

For an unclassified balance sheet, the carrying amount (net of accumulated amortization) as of the balance sheet date of capitalized costs associated with the issuance of debt instruments (for example, legal, accounting, underwriting, printing, and registration costs) that will be charged against earnings over the life of the debt instruments to which such costs pertain.

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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

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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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

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