Subsequent Events - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		0 Months Ended												9 Months Ended	0 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Nov. 03, 2014 Subsequent Event [Member]	Oct. 15, 2014 Subsequent Event [Member]	Oct. 02, 2014 Subsequent Event [Member]	Jul. 10, 2014 Common Stockholders [Member]	Apr. 10, 2014 Common Stockholders [Member]	Jan. 09, 2014 Common Stockholders [Member]	Oct. 09, 2014 Common Stockholders [Member] Subsequent Event [Member]	Jul. 10, 2014 Common Unitholders [Member]	Apr. 10, 2014 Common Unitholders [Member]	Jan. 09, 2014 Common Unitholders [Member]	Oct. 09, 2014 Common Unitholders [Member] Subsequent Event [Member]	Aug. 04, 2014 Dividend Declared [Member]	Sep. 30, 2014 Dividend Declared [Member]	Nov. 10, 2014 Dividend Declared [Member] Subsequent Event [Member]
Subsequent Event [Line Items]
Sale of Sentara Williamsburg office property							$ 15,400,000
Revolving credit facility, borrowed amount						10,000,000
Repayment of revolving credit facility					1,000,000
Dividends paid			$ 15,729,000	$ 2,578,000				$ 3,100,000	$ 3,100,000	$ 3,100,000	$ 4,000,000	$ 2,200,000	$ 2,200,000	$ 2,100,000	$ 2,400,000
Cash dividend/distribution per share, declared	$ 0.16	$ 0.16	$ 0.48	$ 0.24												$ 0.16		$ 0.16
Cash dividend/distribution, date declared																	Aug. 04, 2014	Nov. 10, 2014
Cash dividend/distribution, date of record																	Oct. 01, 2014	Dec. 30, 2014