Notes Payable, Revolving Credit Facility, Interest and Amortization of Deferred Debt Costs - Additional Information (Detail) (USD $)			0 Months Ended	1 Months Ended							6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Apr. 24, 2014 Olney Center	Apr. 30, 2014 Olney Center	Jun. 30, 2014 Van Ness Square	Jun. 30, 2014 Northrock Loan	Jun. 30, 2014 Variable Rate Loans Payable Northrock Loan	Jun. 30, 2014 Variable Rate Loans Payable Metro Pike Center Bank Loan	Jun. 30, 2014 Fixed Rate Mortgage Notes Payable Metro Pike Center	Jun. 30, 2014 Fixed Rate Mortgage Notes Payable Metro Pike Center Bank Loan	Jun. 30, 2014 Unsecured Revolving Credit Facility	Jun. 30, 2014 Unsecured Revolving Credit Facility LIBOR	Jun. 30, 2014 Unsecured Revolving Credit Facility LIBOR Minimum	Jun. 30, 2014 Unsecured Revolving Credit Facility LIBOR Maximum	Jun. 30, 2014 Letter of Credit
Debt Instrument [Line Items]
Notes payable	$ 820,145,000	$ 820,068,000
Debt outstanding with fixed-rate	790,200,000	789,900,000
Debt outstanding with variable-rate	29,900,000	30,200,000
Carrying value of properties collateralizing mortgage notes	901,000,000	907,200,000
Line of credit facility, maximum borrowing capacity											275,000,000				628,000
Line of credit facility maturity date											Jun. 23, 2018
Extension in line of credit facility period											1 year
Line of credit facility, maximum borrowing capacity											274,400,000
Description of variable rate basis											one-month LIBOR
Interest rate spread on LIBOR												1.45%	1.45%	2.00%
Guarantor obligations, maximum exposure, percentage									50.00%
Construction-to-permanent loan					71,600,000
Guarantor obligations, maximum exposure						7,500,000				7,800,000
Amount oustanding							14,662,000	15,248,000
Total outstanding debt		820,100,000
Proceeds from sale of real estate			11,000,000	11,000,000
Sale-leaseback, monthly lease payments			60,400
Annual increase in rental payments, percentage			1.50%	1.50%
Sale-leaseback, fixed interest rate			8.00%
Sales price of property				11,000,000
Sale leaseback, option to purchase the property			$ 14,600,000	$ 14,600,000