Acquisitions and Development Projects (Details)		Nov. 30, 2016 USD ($) ft² a	Oct. 07, 2016 USD ($) ft²	Aug. 10, 2016 USD ($) ft²	Aug. 01, 2016 USD ($) ft² building	Dec. 31, 2016 USD ($) ft² story building	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Number of properties acquired | building						3
Construction in progress						$ 34,825,000	$ 20,975,000
500 TownPark Building [Member]
Business Acquisition [Line Items]
Rentable Square Feet (Unaudited) | ft²	[1]					134,400
Percentage Leased as of Acquisition (Unaudited)						80.00%
Number of stories of office building | story						4
Construction in progress						$ 24,000,000	$ 1,000,000
Enclave Place [Member]
Business Acquisition [Line Items]
Rentable Square Feet (Unaudited) | ft²	[1]					301,000
Line of Credit [Member] | Unsecured Debt [Member] | $500 Million Unsecured 2015 Line of Credit [Member]
Business Acquisition [Line Items]
Proceeds from Unsecured Line of Credit						$ 500,000,000
CNL Center I and CNL Center II [Member]
Business Acquisition [Line Items]
Number of properties acquired | building					2
Percentage ownership of properties acquired					99.00%
Rentable Square Feet (Unaudited) | ft²					622,488
Percentage Leased as of Acquisition (Unaudited)					95.00%
Net Contractual Purchase Price (in millions)					$ 166,700,000
One Wayside Road [Member]
Business Acquisition [Line Items]
Percentage ownership of properties acquired				100.00%
Rentable Square Feet (Unaudited) | ft²				200,605
Percentage Leased as of Acquisition (Unaudited)				100.00%
Net Contractual Purchase Price (in millions)				$ 62,900,000
Galleria 200 Building [Member]
Business Acquisition [Line Items]
Percentage ownership of properties acquired			100.00%
Rentable Square Feet (Unaudited) | ft²			431,614
Percentage Leased as of Acquisition (Unaudited)			89.00%
Net Contractual Purchase Price (in millions)			$ 69,600,000
750 W. John Carpenter Freeway [Member]
Business Acquisition [Line Items]
Percentage ownership of properties acquired	[1]	100.00%
Rentable Square Feet (Unaudited) | ft²	[1]	314,714
Percentage Leased as of Acquisition (Unaudited)	[1]	78.00%
Net Contractual Purchase Price (in millions)	[1]	$ 50,600,000
Number of acres of adjacent developable land | a		3.5

[1] Including 3.5 acres of adjacent developable land.