Indebtedness - Narrative (Details) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended			9 Months Ended		0 Months Ended		0 Months Ended			0 Months Ended		0 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Unsecured revolving credit facility, due October 2015	Sep. 30, 2013 Unsecured revolving credit facility, due October 2015	Jul. 18, 2014 Unsecured revolving credit facility, due October 2015	Sep. 30, 2014 Unsecured term loan, due December 2016	Sep. 30, 2013 Unsecured term loan, due December 2016	Sep. 15, 2014 Senior notes 6.40% Due 2015	Sep. 15, 2014 Senior notes 6.40% Due 2015	Aug. 01, 2014 Mortgage notes maturing from 2015 through 2026	Jun. 27, 2014 Mortgage notes maturing from 2015 through 2026	Sep. 30, 2014 Mortgage notes maturing from 2015 through 2026 property	Aug. 01, 2014 Mortgage Notes Payable 5.68%	Aug. 01, 2014 Mortgage Notes Payable 5.68%	Jun. 27, 2014 Mortgage notes payable, due 2023 at 6.14%	Jun. 27, 2014 Mortgage notes payable, due 2015 at 5.78%	Mar. 11, 2014 Mortgage notes payable, due 2014 at 4.95%	Sep. 30, 2014 One Enterprise Center in Jacksonville, Florida Mortgage notes maturing from 2015 through 2026
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 750,000,000.0
Available borrowing capacity						747,500,000
Outstanding indebtedness									500,000,000.0												40,100,000
Variable rate basis						LIBOR			LIBOR
Basis points on variable rate						1.50%			1.85%
Commitment fee percentage						0.35%
Interest rate payable percentage						1.70%			2.00%
Average interest rate percentage						1.70%	1.70%		2.00%	2.10%
Amount outstanding						0		235,000,000.0
Repayment of debt											33,400,000					265,000,000		11,200,000	8,500,000	12,000,000
Interest rate stated percentage												6.40%					5.68%	6.14%	5.78%	4.95%
Number of real estate properties secured by mortgage															11
Number of buildings secured by mortgage															15
Real estate properties, net	4,898,041,000		4,898,041,000		4,642,106,000										724,400,000
Mortgage notes payable, net	619,760,000		619,760,000		914,510,000										619,760,000
Gain (loss) on early extinguishment of debt	$ 6,699,000	$ 0	$ 6,699,000	$ (60,027,000)									$ 6,700,000	$ (3,300,000)