Property Dispositions and Assets Held for Sale (Property Dispositions) (Details) - USD ($) $ in Thousands														12 Months Ended
	Nov. 29, 2018	Jan. 04, 2018	Jul. 27, 2017	Jul. 05, 2017	Jun. 16, 2017	Dec. 29, 2016	Dec. 22, 2016	Sep. 28, 2016	Jul. 29, 2016	Jul. 27, 2016	May 02, 2016	Apr. 28, 2016	Apr. 21, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net Sales Proceeds, equity method investment														$ 0	$ 12,334	$ 0
Notes receivable														$ 0	$ 0
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 1055 East Colorado Boulevard
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets													$ 29,462
Net Sales Proceeds													$ 60,076
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Fairway Center II
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets												$ 14,406
Net Sales Proceeds												$ 33,062
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 1901 Main Street
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets											$ 29,964
Net Sales Proceeds											63,149
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 1901 Main Street | Notes Receivable | Secured Promissory Note
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Notes receivable											$ 33,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 9221 Corporate Boulevard
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets										$ (192)
Net Sales Proceeds										$ 12,035
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 150 West Jefferson
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets									$ (664)
Net Sales Proceeds									$ 77,844
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 9200 and 9211 Corporate Boulevard
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets								$ (41)
Net Sales Proceeds								$ 12,519
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 11695 Johns Creek Parkway
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets							$ 1,978
Net Sales Proceeds							$ 13,827
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Braker Pointe III
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets						$ 18,579
Net Sales Proceeds						$ 48,006
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Sarasota Commerce Center II
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets					$ 6,493
Net Sales Proceeds					$ 23,090
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Two Independence Square
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets				$ 109,381
Net Sales Proceeds				$ 352,428
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 8560 Upland Drive
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale, equity method investment			$ 3,683
Net Sales Proceeds, equity method investment			$ 12,334
Piedmont’s ownership percentage														72.00%
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 2017 Disposition Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets		$ 45,275
Net Sales Proceeds		419,644
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 800 North Brand Boulevard
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss) on Sale of Real Estate Assets	$ 30,416
Net Sales Proceeds	$ 155,583
Secured Debt | Secured Promissory Note
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Notes receivable		$ 3,200