Property Transactions (Acquisition Pro Forma) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Document Fiscal Year Focus			2013
Revenues	$ 44,158	$ 32,496	$ 84,052	$ 65,873
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	453	6,013	56,951	3,927
Net income	819	10,230	57,725	(1,124)
Net Income (Loss) Available to Common Stockholders, Basic	(5,579)	6,401	47,593	(6,711)
Post Oak Central and Terminus Pro Forma [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenues	44,158	34,845	85,263	70,572
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	453	6,632	57,618	5,163
Net income	819	10,849	58,415	113
Net Income (Loss) Available to Common Stockholders, Basic	$ (5,579)	$ 7,020	$ 48,283	$ (5,474)
Earnings Per Share, Basic	$ (0.05)	$ 0.07	$ 0.43	$ (0.05)
Earnings Per Share, Diluted	$ (0.05)	$ 0.07	$ 0.43	$ (0.05)