The percentage of debt offering price at par value during the period.

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Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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-Publisher SEC
-Name Regulation S-X (SX)
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-Article 12
-Section 13
-Sentence Column B

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Fixed interest rate related to the interest rate derivative.

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Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unsecured Debt - Narrative (Details)	1 Months Ended		3 Months Ended	12 Months Ended
Unsecured Debt - Narrative (Details)	Feb. 21, 2019 USD ($)	Apr. 30, 2013 USD ($)	Sep. 30, 2012 USD ($)	Dec. 31, 2018 USD ($) instrument Option line_of_credit	Dec. 31, 2017 USD ($)	Jan. 31, 2019	Mar. 31, 2018 USD ($)	Apr. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Nov. 30, 2016 USD ($)	Oct. 31, 2016 USD ($)	Apr. 30, 2016	Mar. 31, 2015 USD ($)	Apr. 30, 2014 USD ($)
Debt Instrument [Line Items]
Unamortized debt issuance expense				$ 4,200,000	$ 5,400,000
Number of outstanding lines of credit \| line_of_credit				2
Senior notes				$ 275,000,000	$ 275,000,000
Effective interest rate				4.50%	4.50%
Unsecured debt, net				$ 3,799,316,000	$ 3,501,709,000
Debt instrument, face amount				3,200,000,000	2,900,000,000
Lines of credit				0	179,000,000
Subsequent Event [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage						5.57%
Unsecured Bonds 4.500% [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				300,000,000	0
Unsecured Bonds 3.625% [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				350,000,000	350,000,000
Unsecured Bonds 3.375%, Due April 2026 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				450,000,000	450,000,000
Unsecured Bonds 5.200% [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				300,000,000	300,000,000
Unsecured Bonds 3.375% [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				300,000,000	300,000,000
Unsecured Bonds 3.875% [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				400,000,000	400,000,000
Unsecured Bonds 3.250% [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				300,000,000	300,000,000
Unsecured Bonds 3.625% [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				300,000,000	300,000,000
Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt instrument, unamortized premium				7,100,000	5,200,000
Unamortized debt issuance expense				18,500,000	18,100,000
Unsecured Debt [Member] \| Senior Unsecured Notes Maturing April 1, 2025 [Member]
Debt Instrument [Line Items]
Senior notes				496,500,000	495,900,000
Debt instrument, face amount													$ 500,000,000
Interest rate, stated percentage													3.50%
Debt offering price													99.747%
Line of Credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				1,240,000,000
Line of Credit [Member] \| Line of Credit Working Capital [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				35,000,000.0
Line of Credit [Member] \| Unsecured Line of Credit [Member]
Debt Instrument [Line Items]
Unamortized debt issuance expense				3,900,000	3,200,000
Maximum borrowing capacity				1,200,000,000
Lines of credit				$ 0	$ 179,000,000
Number of extension options \| Option				1
Term extension period				18 months
Line of Credit [Member] \| Unsecured Line of Credit [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on rate				0.875%
Line of Credit [Member] \| Unsecured Line of Credit [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Subsequent Event [Member]
Debt Instrument [Line Items]
Basis spread on rate	0.825%
Line of Credit [Member] \| Working Capital, Unsecured Line of Credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 35,000,000.0
Variable rate term loan [Member]
Debt Instrument [Line Items]
Unsecured debt, net										$ 350,000,000	$ 225,000,000
Weighted average interest rate				3.00%	2.50%
Basis spread on rate				0.95%
Variable rate term loan [Member] \| Carrying Value [Member]
Debt Instrument [Line Items]
Unsecured debt, net				$ 348,813,000	$ 348,545,000
Variable rate term loan [Member] \| Interest Rate Swap [Member]
Debt Instrument [Line Items]
Unsecured debt, net				$ 350,000,000	350,000,000
Number of derivative instruments held \| instrument				5
Term of loan				5 years
Variable rate term loan [Member] \| Variable Term Loan, Tranche One [Member] \| Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, notional amount				$ 175,000,000
Derivative, fixed interest rate				2.30%
Senior Notes [Member] \| BRE Properties, Inc. [Member]
Debt Instrument [Line Items]
Unsecured debt, net				$ 601,300,000	603,200,000
Long-term debt acquired														$ 900,000,000
Senior Notes [Member] \| Unsecured Bonds 4.500% [Member]
Debt Instrument [Line Items]
Unsecured debt, net				$ 295,400,000
Debt instrument, face amount							$ 300,000,000.0
Interest rate, stated percentage				4.50%			4.50%
Debt offering price							99.591%
Senior Notes [Member] \| Unsecured Bonds 3.625% [Member]
Debt Instrument [Line Items]
Unsecured debt, net				$ 345,800,000	345,200,000
Debt instrument, face amount								$ 350,000,000
Interest rate, stated percentage				3.625%
Debt offering price								99.423%
Senior Notes [Member] \| Unsecured Bonds 3.375%, Due April 2026 [Member]
Debt Instrument [Line Items]
Unsecured debt, net				$ 445,000,000	444,400,000
Interest rate, stated percentage				3.375%
Debt offering price												99.386%
Senior Notes [Member] \| Unsecured Bonds 5.500% [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage														5.50%
Face amount of debt paid off									$ 300,000,000
Senior Notes [Member] \| Unsecured Bonds 5.200% [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage				5.20%
Senior Notes [Member] \| Unsecured Bonds 3.375% [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage				3.375%
Senior Notes [Member] \| Unsecured Bonds 3.875% [Member]
Debt Instrument [Line Items]
Unsecured debt, net				$ 396,500,000	395,800,000
Debt instrument, face amount														$ 400,000,000
Interest rate, stated percentage				3.875%										3.875%
Debt offering price														99.234%
Senior Notes [Member] \| Unsecured Bonds 3.250% [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage		3.25%		3.25%
Debt offering price		99.152%
Proceeds from issuance of unsecured debt		$ 300,000,000
Long-term debt, gross				$ 297,600,000	297,000,000
Senior Notes [Member] \| Unsecured Bonds 3.625% [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage			3.625%	3.625%
Debt offering price			98.99%
Proceeds from issuance of unsecured debt			$ 300,000,000
Long-term debt, gross				$ 297,800,000	$ 297,200,000
Senior Notes [Member] \| Unsecured Notes, 4.0 Interest Rate, Due March 2029 [Member] \| Subsequent Event [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 350,000,000
Interest rate, stated percentage	4.00%
Debt offering price	99.188%
Unsecured Line of Credit [Member]
Debt Instrument [Line Items]
Weighted average interest rate				3.20%	2.30%
Lines of credit				$ 0	$ 179,000,000
Unsecured Line of Credit [Member] \| Line of Credit Working Capital [Member]
Debt Instrument [Line Items]
Lines of credit					$ 0