Notes Payable, Revolving Credit Facility, Interest and Amortization of Deferred Debt Costs - Additional Information (Detail) (USD $)			1 Months Ended	9 Months Ended						9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Apr. 30, 2014 Olney Center	Sep. 30, 2014 Olney Center	Sep. 30, 2014 Van Ness Square	Sep. 30, 2014 Northrock Loan	Sep. 30, 2014 Variable Rate Loans Payable Northrock Loan	Sep. 30, 2014 Variable Rate Loans Payable Metro Pike Center Bank Loan	Sep. 30, 2014 Fixed Rate Mortgage Notes Payable Metro Pike Center Bank Loan	Sep. 30, 2014 Unsecured Revolving Credit Facility	Sep. 30, 2014 Unsecured Revolving Credit Facility LIBOR	Sep. 30, 2014 Unsecured Revolving Credit Facility LIBOR Minimum	Sep. 30, 2014 Unsecured Revolving Credit Facility LIBOR Maximum	Sep. 30, 2014 Letter of Credit
Debt Instrument [Line Items]
Outstanding debt	$ 846,465,000
Debt outstanding with fixed-rate	786,700,000	789,900,000
Debt outstanding with variable-rate	59,800,000	30,200,000
Carrying value of properties collateralizing mortgage notes	898,200,000	907,200,000
Line of credit facility, maximum borrowing capacity										275,000,000				448,000
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										244,600,000
Revolving credit facility payable	30,000,000	0								30,000,000
Description of variable rate basis										one-month LIBOR
Interest rate spread on LIBOR											1.45%	1.45%	2.00%
Construction-to-permanent loan					71,600,000
Construction loan	1,859,000	0			1,900,000
Guarantor obligations, maximum exposure						7,500,000			7,800,000
Amount oustanding							14,600,000	15,200,000
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%
Sale-leaseback, fixed interest rate			8.00%
Sales price of property			11,000,000
Sale leaseback, option to purchase the property			14,600,000
Total outstanding debt		$ 820,100,000