Guarantor and Non-Guarantor Financial Information - Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Real estate assets, at cost:
Land	$ 506,389		$ 470,432
Buildings and improvements, less accumulated depreciation	2,325,222		2,121,570
Intangible lease assets, less accumulated amortization	80,979		77,676
Construction in progress	29,920		15,848
Real estate assets held for sale, net	0		331,068
Total real estate assets	2,942,510		3,016,594
Cash and cash equivalents	13,545		4,571	$ 7,382	$ 6,992
Tenant and straight-line receivables, net	159,344		147,562
Investment in subsidiaries	0		0
Notes receivable	0		0
Prepaid expenses, restricted cash, escrows, interest rate swaps, and other assets	27,268		27,353
Goodwill	98,918		98,918
Deferred lease costs, net	275,172		236,198
Other assets held for sale, net	0		61,233
Total assets	3,516,757		3,592,429
Liabilities:
Debt, net	1,481,404		1,685,472
Accounts payable, accrued expenses, dividends payable, interest rate swaps and accrued capital expenditures	149,044		121,550
Deferred income	34,609		28,779
Intangible lease liabilities, net	32,726		35,708
Liabilities held for sale, net	0		8,780
Total liabilities	1,697,783		1,880,289
Equity:
Total stockholders’ equity	1,818,974		1,712,140	$ 1,986,489	$ 2,097,703
Total liabilities and stockholders’ equity	3,516,757		3,592,429
Eliminations
Real estate assets, at cost:
Land	0		0
Buildings and improvements, less accumulated depreciation	(300)		(300)
Intangible lease assets, less accumulated amortization	0		0
Construction in progress	0		0
Real estate assets held for sale, net			0
Total real estate assets	(300)		(300)
Cash and cash equivalents	0		(518)
Tenant and straight-line receivables, net	0		0
Investment in subsidiaries	(4,656,833)		(4,448,625)
Notes receivable	(145,310)		(145,310)
Prepaid expenses, restricted cash, escrows, interest rate swaps, and other assets	(24)		(24)
Goodwill	0		0
Deferred lease costs, net	0		0
Other assets held for sale, net			0
Total assets	(4,802,467)		(4,594,777)
Liabilities:
Debt, net	(145,310)		(145,310)
Accounts payable, accrued expenses, dividends payable, interest rate swaps and accrued capital expenditures	(24)		(542)
Deferred income	0		0
Intangible lease liabilities, net	0		0
Liabilities held for sale, net			0
Total liabilities	(145,334)		(145,852)
Equity:
Total stockholders’ equity	(4,657,133)	$ (4,448,925)	(4,448,925)
Total liabilities and stockholders’ equity	(4,802,467)		(4,594,777)
Piedmont (Parent) (Guarantor) | Reportable Legal Entities
Real estate assets, at cost:
Land	0		0
Buildings and improvements, less accumulated depreciation	0		0
Intangible lease assets, less accumulated amortization	0		0
Construction in progress	0		0
Real estate assets held for sale, net			0
Total real estate assets	0		0
Cash and cash equivalents	150		150
Tenant and straight-line receivables, net	0		0
Investment in subsidiaries	1,845,797		1,744,122
Notes receivable	0		0
Prepaid expenses, restricted cash, escrows, interest rate swaps, and other assets	0		42
Goodwill	0		0
Deferred lease costs, net	0		0
Other assets held for sale, net			0
Total assets	1,845,947		1,744,314
Liabilities:
Debt, net	0		0
Accounts payable, accrued expenses, dividends payable, interest rate swaps and accrued capital expenditures	26,973		32,174
Deferred income	0		0
Intangible lease liabilities, net	0		0
Liabilities held for sale, net			0
Total liabilities	26,973		32,174
Equity:
Total stockholders’ equity	1,818,974		1,712,140
Total liabilities and stockholders’ equity	1,845,947		1,744,314
Piedmont OP (the Issuer) | Reportable Legal Entities
Real estate assets, at cost:
Land	36,094		36,094
Buildings and improvements, less accumulated depreciation	177,798		176,927
Intangible lease assets, less accumulated amortization	0		0
Construction in progress	2,412		5,708
Real estate assets held for sale, net			0
Total real estate assets	216,304		218,729
Cash and cash equivalents	9,674		0
Tenant and straight-line receivables, net	16,450		16,143
Investment in subsidiaries	2,810,875		2,704,337
Notes receivable	810		810
Prepaid expenses, restricted cash, escrows, interest rate swaps, and other assets	6,180		5,682
Goodwill	98,918		98,918
Deferred lease costs, net	16,249		15,158
Other assets held for sale, net			0
Total assets	3,175,460		3,059,777
Liabilities:
Debt, net	1,292,334		1,495,065
Accounts payable, accrued expenses, dividends payable, interest rate swaps and accrued capital expenditures	21,069		15,382
Deferred income	3,505		2,274
Intangible lease liabilities, net	0		0
Liabilities held for sale, net			0
Total liabilities	1,316,908		1,512,721
Equity:
Total stockholders’ equity	1,858,552	$ 1,547,056	1,547,056
Total liabilities and stockholders’ equity	3,175,460		3,059,777
Non-Guarantor Subsidiaries | Reportable Legal Entities
Real estate assets, at cost:
Land	470,295		434,338
Buildings and improvements, less accumulated depreciation	2,147,724		1,944,943
Intangible lease assets, less accumulated amortization	80,979		77,676
Construction in progress	27,508		10,140
Real estate assets held for sale, net			331,068
Total real estate assets	2,726,506		2,798,165
Cash and cash equivalents	3,721		4,939
Tenant and straight-line receivables, net	142,894		131,419
Investment in subsidiaries	161		166
Notes receivable	144,500		144,500
Prepaid expenses, restricted cash, escrows, interest rate swaps, and other assets	21,112		21,653
Goodwill	0		0
Deferred lease costs, net	258,923		221,040
Other assets held for sale, net			61,233
Total assets	3,297,817		3,383,115
Liabilities:
Debt, net	334,380		335,717
Accounts payable, accrued expenses, dividends payable, interest rate swaps and accrued capital expenditures	101,026		74,536
Deferred income	31,104		26,505
Intangible lease liabilities, net	32,726		35,708
Liabilities held for sale, net			8,780
Total liabilities	499,236		481,246
Equity:
Total stockholders’ equity	2,798,581		2,901,869
Total liabilities and stockholders’ equity	$ 3,297,817		$ 3,383,115