Allocation of Purchase Price (Parenthetical) (Detail) (USD $)	3 Months Ended		3 Months Ended
	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2013 Promenade Corporate Center	Mar. 31, 2012 Promenade Corporate Center		Sep. 30, 2012 Gem Llc
Business Acquisition [Line Items]
Purchase Price	$ 76,903,000	$ 30,738,000	$ 52,300,000	$ 52,253,000	[1]
Cash paid to purchase entity			13,900,000			21,200,000
Issuance of common stock for acquisition shares			3,230,769
Fair value of the common stock related to acquisition			39,100,000
Closing price of shares on date of acquisition			$ 12.11
Assets received in connection with property acquisitions	$ 772,000		$ 772,000
Percentage of ownership interest						20.00%

[1] The purchase price of $52.3 million reflects $13.9 million in cash paid and the issuance of 3,230,769 shares of common stock with a fair value of approximately $39.1 million based on a closing price of $12.11 per share on the date of acquisition. The purchase price noted above is net of master lease agreements between the Company and the seller in the amount of $772,000 (included in other assets on the accompanying condensed consolidated balance sheets) based on the estimated fair value of funds expected to be received from escrow in connection with the acquisition. Payments under the master lease agreements commence upon the expiration of two existing leases in June 2012 and February 2013 (with terms through May 2013 and January 2015, respectively) unless the related spaces are re-leased with base rents equaling or exceeding the master lease payments. In addition, the seller has agreed to reimburse the Company for any expenditures resulting from tenant improvements or leasing commissions related to the spaces to the extent that funds remain available pertaining to the master lease agreements. See Note 17 for a discussion of changes in the fair value of this asset after the initial acquisition.