Subsequent Events (Notes)	12 Months Ended
Dec. 31, 2013
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On January 10, 2014, the Company completed an underwritten public offering of 10,500,000 shares of its common stock at the public offering price of $18.15. On February 11, 2014, the Company sold an additional 1,325,000 shares of its common stock at the public offering price of $18.15 pursuant to the exercise of the underwriters’ option to purchase additional shares. The net proceeds from the offering, including shares sold pursuant to the underwriters’ option to purchase additional shares, after deducting the underwriting discount and offering expenses payable by the Company, were approximately $205.5 million and will be used to fund potential acquisition opportunities, to repay amounts outstanding from time to time under the Company’s senior unsecured revolving credit facility and/or for general corporate purposes. On January 17, 2014, the Company sold the Woodbranch Building, a 109,000 square foot office property located in Houston, Texas, for a gross sale price of $15.0 million. The Company received approximately $13.9 million in net proceeds, which were used to fund subsequent acquisitions. The Company expects to book a gain of approximately $10.0 million during the first quarter of 2014. On January 30, 2014, the Company completed the acquisition of the JTB Center, a complex of three office buildings totaling 248,000 square feet located in the Deerwood submarket of Jacksonville, Florida, for a gross purchase price of $33.3 million. As of January 1, 2014, the JTB Center had a combined occupancy of 94.4% and was unencumbered by any secured indebtedness. On January 31, 2014, the Company sold Mesa Corporate Center, a 106,000 square foot office property located in Phoenix, Arizona, for a gross sale price of $13.2 million. the Company received approximately $12.1 million in net proceeds from the sale, which were used to fund subsequent acquisitions. the Company expects to realize a gain of approximately $489,000 during the first quarter of 2014. As a result of its recently completed Mergers, the Company acquired an indirect interest in the Austin joint venture, a joint venture with CalSTRS that owns Frost Bank Tower, One Congress Plaza, One American Center, 300 West 6th Street and San Jacinto Center in the central business district of Austin, Texas. The Company's interest in the CalSTRS joint venture was held through a joint venture with Madison. On January 24, 2014, pursuant to a put right held by Madison, the Company purchased Madison’s approximately 17% interest in the CalSTRS joint venture for a purchase price of approximately $41.5 million. On February 10, 2014, pursuant to an agreement entered into between CalSTRS and the Company, CalSTRS exercised an option to purchase 60% of Madison's former interest on the same terms as the Company for approximately $24.9 million. After giving effect to these transactions, the Company has a 40% interest in the CalSTRS joint venture and the Austin properties, with CalSTRS owning the remaining 60%.

Subsequent Events

On January 10, 2014, the Company completed an underwritten public offering of 10,500,000 shares of its common stock at the public offering price of $18.15. On February 11, 2014, the Company sold an additional 1,325,000 shares of its common stock at the public offering price of $18.15 pursuant to the exercise of the underwriters’ option to purchase additional shares. The net proceeds from the offering, including shares sold pursuant to the underwriters’ option to purchase additional shares, after deducting the underwriting discount and offering expenses payable by the Company, were approximately $205.5 million and will be used to fund potential acquisition opportunities, to repay amounts outstanding from time to time under the Company’s senior unsecured revolving credit facility and/or for general corporate purposes.

On January 17, 2014, the Company sold the Woodbranch Building, a 109,000 square foot office property located in Houston, Texas, for a gross sale price of $15.0 million. The Company received approximately $13.9 million in net proceeds, which were used to fund subsequent acquisitions. The Company expects to book a gain of approximately $10.0 million during the first quarter of 2014.

On January 30, 2014, the Company completed the acquisition of the JTB Center, a complex of three office buildings totaling 248,000 square feet located in the Deerwood submarket of Jacksonville, Florida, for a gross purchase price of $33.3 million. As of January 1, 2014, the JTB Center had a combined occupancy of 94.4% and was unencumbered by any secured indebtedness.

On January 31, 2014, the Company sold Mesa Corporate Center, a 106,000 square foot office property located in Phoenix, Arizona, for a gross sale price of $13.2 million. the Company received approximately $12.1 million in net proceeds from the sale, which were used to fund subsequent acquisitions. the Company expects to realize a gain of approximately $489,000 during the first quarter of 2014.

As a result of its recently completed Mergers, the Company acquired an indirect interest in the Austin joint venture, a joint venture with CalSTRS that owns Frost Bank Tower, One Congress Plaza, One American Center, 300 West 6th Street and San Jacinto Center in the central business district of Austin, Texas. The Company's interest in the CalSTRS joint venture was held through a joint venture with Madison. On January 24, 2014, pursuant to a put right held by Madison, the Company purchased Madison’s approximately 17% interest in the CalSTRS joint venture for a purchase price of approximately $41.5 million. On February 10, 2014, pursuant to an agreement entered into between CalSTRS and the Company, CalSTRS exercised an option to purchase 60% of Madison's former interest on the same terms as the Company for approximately $24.9 million. After giving effect to these transactions, the Company has a 40% interest in the CalSTRS joint venture and the Austin properties, with CalSTRS owning the remaining 60%.