Debt (Narrative) (Details)		3 Months Ended		6 Months Ended
		Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) period	Jun. 30, 2014 USD ($)
Debt Instrument [Line Items]
Interest payments on debt facilities		$ 18,300,000	$ 16,700,000	$ 38,700,000	$ 33,200,000
Capitalized interest		900,000	$ 500,000	$ 1,700,000	$ 800,000
$170 Million Unsecured 2015 Term Loan [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate				1.125%
$170 Million Unsecured 2015 Term Loan [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate				0.90%
$170 Million Unsecured 2015 Term Loan [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate				1.75%
Bridge Loan [Member] | $50 Million Unsecured Term Loan [Member]
Debt Instrument [Line Items]
Face amount of debt instrument		50,000,000		$ 50,000,000
Unsecured Debt [Member] | $500 Million Unsecured Line of Credit [Member]
Debt Instrument [Line Items]
Net borrowings				257,000,000
Repayments				386,000,000
Unsecured Debt [Member] | $170 Million Unsecured 2015 Term Loan [Member]
Debt Instrument [Line Items]
Face amount of debt instrument		170,000,000		$ 170,000,000
Term of loan				3 years
Unsecured Debt [Member] | $170 Million Unsecured 2015 Term Loan [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	[1],[2]			1.125%
Unsecured Debt [Member] | $50 Million Unsecured Term Loan [Member]
Debt Instrument [Line Items]
Face amount of debt instrument		50,000,000		$ 50,000,000
Unsecured Debt [Member] | $50 Million Unsecured Term Loan [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	[2]			1.15%
Secured Debt [Member] | $160 Million Fixed Rate Loan [Member]
Debt Instrument [Line Items]
Face amount of debt instrument		$ 160,000,000		$ 160,000,000
Term of loan				7 years
Rate	[3]	3.48%		3.48%
Period for written notice to prepay outstanding principal balance				30 days
Period from maturity date with no prepayment penalty				90 days
Line of Credit [Member] | Unsecured Debt [Member] | London Interbank Offered Rate (LIBOR), One Month [Member]
Debt Instrument [Line Items]
Duration of interest period				1 month
Line of Credit [Member] | Unsecured Debt [Member] | London Interbank Offered Rate (LIBOR), Two Months [Member]
Debt Instrument [Line Items]
Duration of interest period				2 months
Line of Credit [Member] | Unsecured Debt [Member] | London Interbank Offered Rate (LIBOR), Three Months [Member]
Debt Instrument [Line Items]
Duration of interest period				3 months
Line of Credit [Member] | Unsecured Debt [Member] | London Interbank Offered Rate (LIBOR), Six Months [Member]
Debt Instrument [Line Items]
Duration of interest period				6 months
Line of Credit [Member] | Unsecured Debt [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Duration of interest period				1 month
Line of Credit [Member] | Unsecured Debt [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Duration of interest period				1 year
Line of Credit [Member] | Unsecured Debt [Member] | $500 Million Unsecured Line of Credit [Member]
Debt Instrument [Line Items]
Amount of line of credit		$ 500,000,000		$ 500,000,000
Face amount of debt instrument		500,000,000		$ 500,000,000
Line of Credit [Member] | Unsecured Debt [Member] | $500 Million Unsecured Line of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	[2]			1.175%
Line of Credit [Member] | Unsecured Debt [Member] | $500 Million Unsecured 2015 Line of Credit [Member]
Debt Instrument [Line Items]
Amount of line of credit		500,000,000		$ 500,000,000
Face amount of debt instrument		500,000,000		$ 500,000,000
Term of loan				4 years
Maximum extension period				1 year
Number of extension periods | period				2
Extension period				6 months
Additional increase to new facility under certain terms of the agreement		500,000,000		$ 500,000,000
Aggregate size of new facility		$ 1,000,000,000		$ 1,000,000,000
Unencumbered interest coverage ratio		1.75		1.75
Unencumbered leverage ratio		1.60		1.60
Fixed charge coverage ratio		1.50		1.50
Leverage ratio		0.60		0.60
Secured debt ratio		0.40		0.40
Line of Credit [Member] | Unsecured Debt [Member] | $500 Million Unsecured 2015 Line of Credit [Member] | Federal Funds Rate [Member]
Debt Instrument [Line Items]
Basis spread on variable rate				0.50%
Line of Credit [Member] | Unsecured Debt [Member] | $500 Million Unsecured 2015 Line of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	[2],[4]			1.00%
Line of Credit [Member] | Unsecured Debt [Member] | $500 Million Unsecured 2015 Line of Credit [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate				0.875%
Line of Credit [Member] | Unsecured Debt [Member] | $500 Million Unsecured 2015 Line of Credit [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate				1.55%
Swing Line Sub Facility [Member] | Unsecured Debt [Member] | $500 Million Unsecured 2015 Line of Credit [Member]
Debt Instrument [Line Items]
Amount of line of credit		$ 50,000,000		$ 50,000,000

[1] On a periodic basis, Piedmont may select from multiple interest rate options, including the prime rate and various-length LIBOR locks. All LIBOR selections are subject to an additional spread (1.125% as of June 30, 2015) over the selected rate based on Piedmont’s current credit rating. The principal balance as of June 30, 2015 consisted of the 30-day LIBOR rate of 0.19% (subject to the additional spread mentioned above).

[2] Other than the $35 Million Fixed-Rate Loan, all of Piedmont’s outstanding debt as of June 30, 2015 and December 31, 2014 is interest-only.

[3] The $160 Million Fixed-Rate Loan has a fixed coupon rate of 3.48%, however, after consideration of the impact of settled interest rate swap agreements, the effective interest rate on this debt is 3.58%.

[4] Piedmont may select from multiple interest rate options with each draw, including the prime rate and various-length LIBOR locks. All LIBOR selections are subject to an additional spread (1.00% as of June 30, 2015) over the selected rate based on Piedmont’s current credit rating. The outstanding balance as of June 30, 2015 consisted of 30-day LIBOR draws at a rate of 0.19% (subject to the additional spread mentioned above).