Subsequent Events	6 Months Ended
Jun. 30, 2013
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS The Company entered into two purchase and sale contracts on July 19, 2013, to purchase Greenway Plaza, a 10-building, approximately 4.4 million square foot office complex in Houston, Texas and 777 Main Street, an approximately 980,000 square foot Class A office building in downtown Fort Worth, Texas (the “Texas Acquisition”). The aggregate purchase price for the Texas Acquisition is approximately $1.1 billion, before adjustment for brokers fees, transfer taxes and other customary closing costs. The assets are expected to be wholly-owned by the Company and remain unencumbered of debt at closing. The Company expects to close the Texas Acquisition in the third quarter of 2013 and to fund the Texas Acquisition through a combination of net proceeds from an equity issuance, proceeds from the expected sale of existing owned properties, proceeds from new secured property-level debt the Company expects to obtain and, on an interim basis, funds drawn under a new $950 million term loan facility described below. On July 29, 2013, the Company entered into a Loan Agreement with JPMorgan Chase Bank, N.A. and Bank of America, N.A. which would permit it to draw up to $950 million, with an accordion feature permitting it, under certain conditions, to increase the amount available by up to $150 million (the “Term Loan”). The Term Loan matures on the first anniversary of the closing of the Texas Acquisition, with two one-year extension options (which during the first one-year extension only up to $500 million can be extended and for the second one-year extension only up to $375 million can be extended). The Company expects the Term Loan will be funded, to the extent necessary, in a single draw-down concurrently with the closing of the Texas Acquisition. The funding of the Term Loan is subject to customary conditions, including the closing of the Texas Acquisition, the absence of any material adverse change in the Company's business or financial condition and its compliance with the financial covenants on a pro forma basis after giving effect to the Texas Acquisition and the related debt and equity financings and asset dispositions. The Term Loan contains financial covenants that are consistent with those of the Company's Credit Facility.

SUBSEQUENT EVENTS

The Company entered into two purchase and sale contracts on July 19, 2013, to purchase Greenway Plaza, a 10-building, approximately 4.4 million square foot office complex in Houston, Texas and 777 Main Street, an approximately 980,000 square foot Class A office building in downtown Fort Worth, Texas (the “Texas Acquisition”). The aggregate purchase price for the Texas Acquisition is approximately $1.1 billion, before adjustment for brokers fees, transfer taxes and other customary closing costs. The assets are expected to be wholly-owned by the Company and remain unencumbered of debt at closing. The Company expects to close the Texas Acquisition in the third quarter of 2013 and to fund the Texas Acquisition through a combination of net proceeds from an equity issuance, proceeds from the expected sale of existing owned properties, proceeds from new secured property-level debt the Company expects to obtain and, on an interim basis, funds drawn under a new $950 million term loan facility described below.

On July 29, 2013, the Company entered into a Loan Agreement with JPMorgan Chase Bank, N.A. and Bank of America, N.A. which would permit it to draw up to $950 million, with an accordion feature permitting it, under certain conditions, to increase the amount available by up to $150 million (the “Term Loan”). The Term Loan matures on the first anniversary of the closing of the Texas Acquisition, with two one-year extension options (which during the first one-year extension only up to $500 million can be extended and for the second one-year extension only up to $375 million can be extended). The Company expects the Term Loan will be funded, to the extent necessary, in a single draw-down concurrently with the closing of the Texas Acquisition.

The funding of the Term Loan is subject to customary conditions, including the closing of the Texas Acquisition, the absence of any material adverse change in the Company's business or financial condition and its compliance with the financial covenants on a pro forma basis after giving effect to the Texas Acquisition and the related debt and equity financings and asset dispositions. The Term Loan contains financial covenants that are consistent with those of the Company's Credit Facility.