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Borrowings (Textual) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Debt Instrument [Line Items] |  |  |
Notes Payable | $ 4,530,000 | $ 4,502,057 |
Average interest rate (percentage) | 3.80% |  |
Mortgages |  |  |
Debt Instrument [Line Items] |  |  |
Average interest rate (percentage) | 4.44% |  |
Proceeds from Issuance of Secured Debt | $ 172,000 |  |
Debt Instrument, Periodic Payment, Principal | 10,600 |  |
Unsecured Debt |  |  |
Debt Instrument [Line Items] |  |  |
Notes Payable | $ 4,053,302 | 3,525,765 |
Average interest rate (percentage) | 3.70% |  |
Unsecured Debt | $1 billion unsecured revolving credit facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, amount outstanding | $ 540,000 |  |
Line of Credit Facility, Current Borrowing Capacity | $ 1,000,000 |  |
Unsecured Debt | $1 billion unsecured revolving credit faciltiy [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Average interest rate (percentage) | 3.42% |  |
Letters of credit outstanding amount | $ 4,200 |  |
Unsecured Debt | Variable Rate Debt [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Average interest rate (percentage) | 3.30% |  |
Unsecured Debt | $ 600,000 | 300,000 |
Unsecured Debt | KeyBank Term Loan [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Face Amount | $ 150,000 |  |
Unsecured Debt | Wells Fargo Term Loan 2022 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate, stated percentage | 2.32% |  |
Debt Instrument, Face Amount | $ 300,000 |  |
Unsecured Debt | Wells Fargo Term Loan 2018 [Domain] |  |  |
Debt Instrument [Line Items] |  |  |
Repayments of Unsecured Debt | 250,000 |  |
Unsecured Debt | US Bank Term Loan [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Face Amount | 150,000 |  |
Unsecured Debt | Private Placement [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Face Amount | $ 242,000 |  |
Unsecured Debt | 4.2% Notes due 2028 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Average interest rate (percentage) | 4.21% |  |
Proceeds from Unsecured Notes Payable | $ 395,000 |  |
Settlement of Forward Swaps | $ 200,000 |  |
Interest rate, stated percentage | 4.20% |  |
Debt Instrument, Issue Price | 99.403% |  |
Debt Instrument, Unamortized Discount, Current | $ 2,400 |  |
Other Underwriting Expense | 2,600 |  |
Debt Instrument, Face Amount | $ 400,000 |  |
Debt Instrument, Term | 10 years |  |
Unsecured Debt | Minimum | $1 billion unsecured revolving credit facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Basis Spread on Variable Rate | 0.85% |  |
Unsecured Debt | Minimum | KeyBank Term Loan [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Basis Spread on Variable Rate | 0.90% |  |
Unsecured Debt | Minimum | Wells Fargo Term Loan 2022 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Basis Spread on Variable Rate | 0.90% |  |
Unsecured Debt | Minimum | Wells Fargo Term Loan 2019 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Basis Spread on Variable Rate | 0.75% |  |
Unsecured Debt | Minimum | US Bank Term Loan [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Basis Spread on Variable Rate | 0.90% |  |
Unsecured Debt | Maximum | $1 billion unsecured revolving credit facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, maximum borrowing capacity | $ 1,500,000 |  |
Debt Instrument, Basis Spread on Variable Rate | 1.55% |  |
Unsecured Debt | Maximum | KeyBank Term Loan [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Basis Spread on Variable Rate | 1.75% |  |
Unsecured Debt | Maximum | Wells Fargo Term Loan 2022 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Basis Spread on Variable Rate | 1.75% |  |
Unsecured Debt | Maximum | Wells Fargo Term Loan 2019 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Basis Spread on Variable Rate | 1.65% |  |
Unsecured Debt | Maximum | US Bank Term Loan [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Basis Spread on Variable Rate | 1.90% |  |
Unsecured Debt | Variable Rate Debt [Member] | $1 billion unsecured revolving credit faciltiy [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Average interest rate (percentage) | 3.40% |  |
Line of credit facility, amount outstanding | $ 540,000 | 410,000 |
Unsecured Debt | Fixed Rate Debt |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Term | 6 years 5 months 15 days |  |
Unsecured Debt | Fixed Rate Debt | Senior Notes |  |  |
Debt Instrument [Line Items] |  |  |
Average interest rate (percentage) | 4.00% |  |
Debt Instrument, Face Amount | $ 2,642,000 | 2,292,000 |
Unsecured Debt | Fixed Rate Debt | Public Income Notes [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Face Amount | 2,400,000 |  |
Unsecured Debt | Fixed Rate Debt | Private Placement [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Face Amount | 242,000 |  |
Repayments of Unsecured Debt | $ 50,000 |  |
Unsecured Debt | Fixed Rate Debt | Minimum |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Term | 7 years |  |
Unsecured Debt | Fixed Rate Debt | Maximum |  |  |
Debt Instrument [Line Items] |  |  |
Debt Instrument, Term | 12 years |  |
Secured Debt [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Average interest rate (percentage) | 4.60% |  |
Secured Debt [Member] | FNMA |  |  |
Debt Instrument [Line Items] |  |  |
Repayments of Secured Debt | $ 80,000 |  |
Secured Debt [Member] | Fixed Rate Debt | Mortgages |  |  |
Debt Instrument [Line Items] |  |  |
Average interest rate (percentage) | 4.60% |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate | $ 476,161 | 882,752 |
Parent Company [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Unsecured Debt | 4,053,302 | 3,525,765 |
Proceeds from notes payable | 869,630 | $ 597,480 | $ 300,000
Highlands of West Village [Member] | Mortgages |  |  |
Debt Instrument [Line Items] |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate | 38,300 |  |
Colonial Grand at Liberty Park [Member] | Mortgages |  |  |
Debt Instrument [Line Items] |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate | 350,000 |  |
Post Hyde Park [Member] | Mortgages |  |  |
Debt Instrument [Line Items] |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate | $ 179,700 |  |

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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -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 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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