Guarantor and Non-Guarantor Financial Information (Balance Sheets) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets:
Land	$ 506,440			$ 470,432
Buildings and improvements, less accumulated depreciation	2,327,055			2,121,570
Intangible lease assets, less accumulated amortization	88,371			77,676
Construction in progress	13,866			15,848
Real estate assets held for sale, net	213,094			331,068
Total real estate assets	3,148,826			3,016,594
Cash and cash equivalents	10,284			4,571	$ 6,807			$ 7,382
Tenant and straight-line rent receivables	157,288			147,562
Investment in subsidiaries	0			0
Notes receivable	0			0
Prepaid expenses, restricted cash, escrows, interest rate swaps, and other assets	28,963			27,353
Goodwill	98,918			98,918
Deferred lease costs, net	267,616			236,198
Other assets held for sale, net	40,036			61,233
Total assets	3,751,931			3,592,429
Liabilities:
Debt, net	1,879,244			1,685,472
Accounts payable, accrued expenses, interest rate swaps and accrued capital expenditures	114,812			121,550
Deferred income	27,985			28,779
Intangible lease liabilities, net	34,970			35,708
Interest rate swaps	6,862			839
Other liabilities held for sale	7,275			8,780
Total liabilities	2,071,148			1,880,289
Equity:
Total stockholders’ equity	1,680,783	$ 1,702,975	$ 1,723,522	1,712,140	$ 1,733,996	$ 1,743,056	$ 1,789,588	$ 1,986,489
Total liabilities and stockholders’ equity	3,751,931			3,592,429
Eliminations
Assets:
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			0
Total real estate assets	(300)			(300)
Cash and cash equivalents	0			(518)
Tenant and straight-line rent receivables	0			0
Investment in subsidiaries	(4,718,747)			(4,448,625)
Notes receivable	(145,310)			(145,310)
Prepaid expenses, restricted cash, escrows, interest rate swaps, and other assets	(9)			(24)
Goodwill	0			0
Deferred lease costs, net	0			0
Other assets held for sale, net	0			0
Total assets	(4,864,366)			(4,594,777)
Liabilities:
Debt, net	(145,310)			(145,310)
Accounts payable, accrued expenses, interest rate swaps and accrued capital expenditures	(9)			(542)
Deferred income	0			0
Intangible lease liabilities, net	0			0
Interest rate swaps	0
Other liabilities held for sale	0			0
Total liabilities	(145,319)			(145,852)
Equity:
Total stockholders’ equity	(4,719,047)			(4,448,925)
Total liabilities and stockholders’ equity	(4,864,366)			(4,594,777)
Piedmont (Parent) (Guarantor) | Reportable Legal Entities
Assets:
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			0
Total real estate assets	0			0
Cash and cash equivalents	150			150
Tenant and straight-line rent receivables	0			0
Investment in subsidiaries	1,681,492			1,744,122
Notes receivable	0			0
Prepaid expenses, restricted cash, escrows, interest rate swaps, and other assets	35			42
Goodwill	0			0
Deferred lease costs, net	0			0
Other assets held for sale, net				0
Total assets	1,681,677			1,744,314
Liabilities:
Debt, net	0			0
Accounts payable, accrued expenses, interest rate swaps and accrued capital expenditures	894			32,174
Deferred income	0			0
Intangible lease liabilities, net	0			0
Interest rate swaps	0
Other liabilities held for sale	0			0
Total liabilities	894			32,174
Equity:
Total stockholders’ equity	1,680,783			1,712,140
Total liabilities and stockholders’ equity	1,681,677			1,744,314
Piedmont OP (the Issuer) | Reportable Legal Entities
Assets:
Land	36,094			36,094
Buildings and improvements, less accumulated depreciation	186,269			176,927
Intangible lease assets, less accumulated amortization	0			0
Construction in progress	1,058			5,708
Real estate assets held for sale, net	0			0
Total real estate assets	223,421			218,729
Cash and cash equivalents	5,758			0
Tenant and straight-line rent receivables	16,514			16,143
Investment in subsidiaries	3,037,093			2,704,337
Notes receivable	810			810
Prepaid expenses, restricted cash, escrows, interest rate swaps, and other assets	6,227			5,682
Goodwill	98,918			98,918
Deferred lease costs, net	16,567			15,158
Other assets held for sale, net	0			0
Total assets	3,405,308			3,059,777
Liabilities:
Debt, net	1,689,749			1,495,065
Accounts payable, accrued expenses, interest rate swaps and accrued capital expenditures	16,054			15,382
Deferred income	3,693			2,274
Intangible lease liabilities, net	0			0
Interest rate swaps	6,862
Other liabilities held for sale	0			0
Total liabilities	1,716,358			1,512,721
Equity:
Total stockholders’ equity	1,688,950			1,547,056
Total liabilities and stockholders’ equity	3,405,308			3,059,777
Non-Guarantors | Reportable Legal Entities
Assets:
Land	470,346			434,338
Buildings and improvements, less accumulated depreciation	2,141,086			1,944,943
Intangible lease assets, less accumulated amortization	88,371			77,676
Construction in progress	12,808			10,140
Real estate assets held for sale, net	213,094			331,068
Total real estate assets	2,925,705			2,798,165
Cash and cash equivalents	4,376			4,939
Tenant and straight-line rent receivables	140,774			131,419
Investment in subsidiaries	162			166
Notes receivable	144,500			144,500
Prepaid expenses, restricted cash, escrows, interest rate swaps, and other assets	22,710			21,653
Goodwill	0			0
Deferred lease costs, net	251,049			221,040
Other assets held for sale, net	40,036			61,233
Total assets	3,529,312			3,383,115
Liabilities:
Debt, net	334,805			335,717
Accounts payable, accrued expenses, interest rate swaps and accrued capital expenditures	97,873			74,536
Deferred income	24,292			26,505
Intangible lease liabilities, net	34,970			35,708
Interest rate swaps	0
Other liabilities held for sale	7,275			8,780
Total liabilities	499,215			481,246
Equity:
Total stockholders’ equity	3,030,097			2,901,869
Total liabilities and stockholders’ equity	$ 3,529,312			$ 3,383,115