Equity Based Compensation Plans, Long term incentive plans (Details) (USD $)	12 Months Ended			0 Months Ended	3 Months Ended	1 Months Ended	12 Months Ended	0 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 09, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2011	Dec. 10, 2013	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 8,740,000	$ 4,508,000	$ 4,141,000
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years
2015 LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)				44,750
Units issued subject only to performance measurement				24,000
Stock-based compensation expense					2,400,000
Vesting percentage of units per year	20.00%
Conversion Ratio, Incentive Units	1
Share Based Compensation Arrangement By Share Based Payment Award, Liquidity Measurement Period	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Measurement Period	10 years
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	10 years 6 months
Series Z Incentive Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)						50,500	154,500
Award vesting period						4 years
Incentive units conversion ratio							one-for-one
Basis for estimating fair value of a unit	The estimated fair value of a Z Unit is determined on the grant date and considers the Company's current stock price, the dividends that are not paid on unvested units and a marketability discount for the 8to 15 years of illiquidity.
Basis for calculating compensation expense	Compensation expense is calculated by multiplying estimated vesting increases for the period by the estimated fair value as of the grant date less its $1.00 per unit purchase price.
Conversion ratchet increase for shares issued prior to 2010	Effective January 1 of each year for each participating executive who remains employed by the Company if the Company has met a specified “funds from operations” per share target, or such other target as the Compensation Committee deems appropriate, for the prior year, up to a maximum conversion ratchet of 100%.
Incentive units conversion threshold			Convertible into common stock of the Company) upon the earlier to occur of 100 percent vesting of the units or the year 2026.
Conversion ratchet increase for shares issued in 2010			The conversion ratchet (accounted for as vesting) of the 2011 Z-1 Units into common units, increased to 10 percent effective January 1, 2012 because the Company achieved the FFO minimum target of $5.65 per diluted share in 2011.  Each year thereafter, vesting of the 2011 Z-1 Units will be consistent with the Company’s annual FFO growth, but is not to be less than zero or greater than 14 percent.
Decrease amount in estimated fair value (in dollars per share)		$ 1.00
Conversion Ratio, Incentive Units							1
Series Z Incentive Units [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	8 years
Vesting percentage of units per year							0.00%
Series Z Incentive Units [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	15 years
Vesting percentage of units per year							14.00%
2014 LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage for 2011 Z 1 Units to be convertible							100.00%
Vesting percentage of units per year						25.00%
Percentage of performance based vesting of 2014 Ltip Units eligible to be earned on absolute total stockholders return								0.33%
Percentage of performance based vesting of 2014 Ltip Units eligible to be earned on relative total stockholders return								0.66%
Conversion Ratio, Incentive Units	1
Share Based Compensation Arrangement By Share Based Payment Award, Liquidity Measurement Period	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Measurement Period	10 years
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	4 years 2 months 12 days
Long Term Incentive Plans - Z Units and 2014 LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	44,750	50,500	0
Maximum number of shares (units) authorized for issuance (in shares)	600,000				600,000
Stock-based compensation expense	6,000,000	2,200,000	2,100,000
Stock-based compensation capitalized	400,000	500,000	500,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	68,800,000				68,800,000
Unrecognized compensation cost	11,700,000				11,700,000
2010 Series Z-1 Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion ratchet increase for shares issued in 2010									The conversion ratchet (accounted for as vesting) of the 2010 Z-1 Units into common units, increased to 20 percent effective January 1, 2011 because the Company achieved the FFO minimum target of $4.75 per diluted share in 2010.  Once the units are vested, Z-1 Unit holders receive quarterly distributions of approximately the dividend rate paid on common shares.  Each year thereafter, vesting of the 2010 Z-1 Units will be consistent with the Company’s annual FFO growth, but is not to be less than zero or greater than 14 percent.
BRE Properties, Inc. [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	3,600,000
Merger and integration expenses	$ 1,700,000