Stockholders' Equity (Details) (USD $)	0 Months Ended			12 Months Ended			0 Months Ended					1 Months Ended	3 Months Ended	0 Months Ended
	Oct. 02, 2014	Feb. 11, 2014	Jun. 05, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 19, 2013	Mar. 25, 2013	Dec. 10, 2012	May 18, 2011	Aug. 12, 2010	Jun. 30, 2003	Jun. 30, 2013	Oct. 02, 2014	Sep. 26, 2014	Jan. 10, 2014	May 28, 2014	Aug. 01, 2012
Class of Stock [Line Items]
Stock issued				23,716,900	31,049,976	18,951,700
Payments for preferred stock redemption				$ 0	$ 135,532,000	$ 0
Preferred stock redemption premium					6,604,000
Preferred dividends declared (in usd per share)				$ 0	$ 0.63	$ 2.00
Shares issued in TPGI merger				0	331,260,000	0
Transaction costs on equity issuance			13,900,000
Stock issued in lieu of director's fees				19,122	26,098	18,399
Share price							18.05
Proceeds from common stock issuance	204,800,000	205,200,000
Common stock, par value (in usd per share)				$ 0.001	$ 0.001		0.001
Merger common stock exchange ratio							0.3822
Limited voting stock, par value (in usd per share)				$ 0.001	$ 0.001		0.001
Partnership Merger
Class of Stock [Line Items]
LP Units issued in Merger							4,451,461
Parent Merger
Class of Stock [Line Items]
Common stock issued in merger (in shares)							17,820,962
Limited voting stock issued in merger (in shares)							4,451,461
Public offering
Class of Stock [Line Items]
Stock issued								11,000,000	13,500,000
Share price								$ 17.25	$ 13.00
Proceeds from common stock issuance								209,000,000	184,800,000
Over-Allotment Option
Class of Stock [Line Items]
Stock issued								1,650,000	1,200,000
At-the-Market
Class of Stock [Line Items]
Proceeds from common stock issuance				8,000,000
Common stock amount authorized																	150,000,000.0
Series D Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Stock issued										1,000,000	1,970,000	2,400,000
Preferred stock yield rate								8.00%		8.00%	8.50%	8.00%
Proceeds from issuance of preferred stock										26,000,000		58,000,000
Stock sale price (in usd per share)										$ 25.00	$ 23.757
Preferred stock, shares outstanding						5,400,000
Preferred stock, liquidation value (in usd per share)						$ 25
Payments for preferred stock redemption													136,300,000
Preferred stock redemption premium													6,600,000
Preferred dividends declared (in usd per share)					$ 0.63	$ 2.00
Common Stock
Class of Stock [Line Items]
Stock issued		1,325,000												1,500,000	10,000,000	10,500,000
Common stock issued in merger (in shares)			4,300,000
Shares issued in TPGI merger			48,400,000
Stock issued in lieu of director's fees						11,733
Common dividends paid						5,000,000
Share price	$ 18.60	$ 18.15												$ 18.60	$ 18.60	$ 18.15
Common Stock | At-the-Market
Class of Stock [Line Items]
Stock issued				391,900
Sales commissions and fees				122,000
Series E Preferred Stock
Class of Stock [Line Items]
Common stock issued in merger (in shares)			13,500,000
Liquidation value on preferred stock			151,600,000
Stock issued in lieu of director's fees						6,666
Preferred dividends paid						$ 1,000,000
Common shares issued upon conversion of preferred shares																		1
Thomas Properties Group, Inc.
Class of Stock [Line Items]
Common stock, par value (in usd per share)							0.01
Limited voting stock, par value (in usd per share)							0.01
Maximum | At-the-Market
Class of Stock [Line Items]
Sale commissions on percent of stock sale price (percent)																	2.00%