Equity - Narrative (Details)						1 Months Ended		3 Months Ended			9 Months Ended		12 Months Ended
	Jul. 21, 2016 shares	May 10, 2016 shares	Apr. 10, 2015 shares	Apr. 01, 2015 ft² shares	Jan. 20, 2015 USD ($) $ / shares shares	Jul. 31, 2016 shares	May 31, 2016 shares	Sep. 30, 2016 ft² building $ / shares shares	Sep. 30, 2015 ft² $ / shares	Mar. 31, 2015 $ / shares shares	Sep. 30, 2016 USD ($) ft² building $ / shares shares	Sep. 30, 2015 USD ($) ft² $ / shares	Dec. 31, 2015 ft² shares	Jan. 20, 2016 USD ($)	Dec. 10, 2015 $ / shares	Jan. 07, 2015
Class of Stock [Line Items]
Common units held by noncontrolling interests (in shares)								26,983,719			26,983,719		56,296,315
Proceeds from sale of common stock (in shares)		10,117,223	6,037,500		11,000,000
Area of real estate property (in square feet) | ft²								820,587	483,862		820,587	483,862
Price per share (in dollars per share) | $ / shares					$ 31.75
Proceeds from issuance of common stock, net | $					$ 385,600,000						$ 880,514,000	$ 380,803,000
Stock repurchase program authorized | $														$ 100,000,000
Common dividends declared (in usd per share) | $ / shares								$ 0.2	$ 0.125		$ 0.6	$ 0.375
At-the-Market
Class of Stock [Line Items]
Proceeds from sale of common stock (in shares)											165,000
Proceeds from issuance of common stock, net | $											$ 20,100,000
Maximum shares authorized, value | $											$ 125,000,000
At-the-Market | Minimum
Class of Stock [Line Items]
Price per share (in dollars per share) | $ / shares								33.54			$ 33.54
At-the-Market | Maximum
Class of Stock [Line Items]
Price per share (in dollars per share) | $ / shares								$ 33.95			$ 33.95
Series B Preferred Stock
Class of Stock [Line Items]
Interest rate of preferred stock (as a percent)										8.375%	8.375%
Shares outstanding of preferred stock (in shares)										5,800,000
Liquidation preference of preferred stock (dollars per share) | $ / shares										$ 25					$ 25.00
Par value of preferred stock (in dollars per share) | $ / shares										$ 0.01
Pinnacle JV
Class of Stock [Line Items]
Number of buildings in property | building								2			2
Area of real estate property (in square feet) | ft²								625,640			625,640
Ownership interest in property (as a percent)								65.00%	65.00%		65.00%	65.00%	65.00%
Canada Pension Plan Investment Board
Class of Stock [Line Items]
Ownership interest in property (as a percent)								55.00%			55.00%					45.00%
EOP Northern California Portfolio
Class of Stock [Line Items]
Area of real estate property (in square feet) | ft²				8,200,000									8,200,000
Consideration transferred, common units (in shares)				63,474,791
Performance units
Class of Stock [Line Items]
Conversion ratio											1
Public Offering, Exercise of Over-allotment Option
Class of Stock [Line Items]
Proceeds from sale of common stock (in shares)					1,650,000
Common Units
Class of Stock [Line Items]
Shares used for valuation of redemption (in shares)											1
Conversion ratio											1
Proceeds from sale of common stock (in shares)											29,477,596		12,650,000
Number of shares redeemed during the period (in shares)	19,000,000						10,000,000
Common Units | EOP Northern California Portfolio
Class of Stock [Line Items]
Consideration transferred, common units (in shares)				8,626,311
Common Units | Secondary Public Offering
Class of Stock [Line Items]
Number of shares redeemed during the period (in shares)						19,195,373
6.25% series A cumulative redeemable preferred units of the Operating Partnership
Class of Stock [Line Items]
Interest rate of preferred stock (as a percent)											6.25%
Shares outstanding of preferred stock (in shares)								407,066			407,066
Liquidation preference of preferred stock (dollars per share) | $ / shares								$ 25			$ 25
Preferred dividends declared (dollars per share) | $ / shares								$ 0.3906