Debt (Details) (USD $)	Sep. 30, 2013		May 09, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Weighted Average Rate	4.04%	[1],[2]
Amount Outstanding	$ 1,823,175,000	[2]		$ 1,416,525,000	[2]
Secured Debt [Member]
Debt Instrument [Line Items]
Weighted Average Rate	5.17%	[1],[2]
Amount Outstanding	987,525,000	[2]		987,525,000	[2]
Unsecured Debt [Member]
Debt Instrument [Line Items]
Weighted Average Rate	2.71%	[1],[2]
Amount Outstanding	835,650,000	[2]		429,000,000	[2]
Mortgage Note $200 Million [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Rate	4.87%	[1]
Amount Outstanding	200,000,000			200,000,000
Face amount of debt instument	200,000,000
Mortgage Note $25 Million [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Rate	5.70%	[1]
Amount Outstanding	25,000,000			25,000,000
Face amount of debt instument	25,000,000
Secured Pooled Facility [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Rate	4.84%	[1],[3]
Amount Outstanding	350,000,000			350,000,000
Number of properties in collateralized pool	9
Face amount of debt instument	350,000,000
Fixed-Rate $105 Million Loan [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Rate	5.29%	[1]
Amount Outstanding	105,000,000			105,000,000
Face amount of debt instument	105,000,000
Fixed-Rate $125 Million Loan [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Rate	5.50%	[1],[4]
Amount Outstanding	125,000,000			125,000,000
Number of properties in collateralized pool	4
Face amount of debt instument	125,000,000
Fixed-Rate $42.5 Million Loan [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Rate	5.70%	[1]
Amount Outstanding	42,525,000			42,525,000
Face amount of debt instument	42,500,000.0
WDC Mortgage Notes $140 Million[Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Rate	5.76%	[1]
Amount Outstanding	140,000,000			140,000,000
Face amount of debt instument	140,000,000
$300 Million Unsecured Term Loan [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Amount Outstanding	300,000,000			300,000,000
Face amount of debt instument	300,000,000
Basis spread on variable rate	1.45%	[1],[5]
$500 Million Unsecured Line of Credit [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Line of credit, effective interest rate	1.36%	[1],[6]
Amount Outstanding	187,000,000			129,000,000
Face amount of debt instument	500,000,000
Borrowing capacity of line of credit	500,000,000
$500 Million Unsecured Line of Credit [Member] | Unsecured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
LIBOR rate in effect	0.18%
$500 Million Unsecured Line of Credit [Member] | Unsecured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
LIBOR rate in effect	0.19%
$350 Million Senior Notes [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Rate	3.40%	[1],[7]
Amount Outstanding	348,650,000			0
Face amount of debt instument	$ 350,000,000		$ 350,000,000
Effective interest rate	3.45%	[1]
Interest Rate Swap [Member] | $300 Million Unsecured Term Loan [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Effective interest rate	2.69%
LIBOR [Member] | $500 Million Unsecured Line of Credit [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.175%

[1] All of Piedmont’s outstanding debt as of September 30, 2013 and December 31, 2012 is interest-only debt.

[2] Weighted average is based on contractual balance of outstanding debt and interest rates in the table as of September 30, 2013, except for the $350 Million Senior Notes, which were issued at a discount (see footnote 7 below).

[3] Nine property collateralized pool includes: 1200 Crown Colony Drive, Braker Pointe III, 2 Gatehall Drive, One and Two Independence Square, 2120 West End Avenue, 400 Bridgewater Crossing, 200 Bridgewater Crossing, and Fairway Center II.

[4] Four property collateralized pool includes 1430 Enclave Parkway, Windy Point I and II, and 1055 East Colorado Boulevard.

[5] The $300 Million Unsecured Term Loan has a stated variable rate; however, Piedmont entered into interest rate swap agreements which effectively fix, exclusive of changes to Piedmont's credit rating, the rate on this facility to 2.69%.

[6] 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 (1.175% as of September 30, 2013) over the selected rate based on Piedmont’s current credit rating. The outstanding balance as of September 30, 2013 consisted of 30-day LIBOR draws ranging from 0.18% to 0.19% (subject to the additional spread mentioned above).

[7] The $350 Million Senior Notes have a fixed coupon rate of 3.40%, however, as a result of the issuance of the notes at a discount, Piedmont recognizes an effective interest rate on this debt issuance of 3.45%.