Subsequent Events (Detail)			3 Months Ended		12 Months Ended
	May 02, 2017 USD ($) ft²	Apr. 28, 2017 USD ($) ft² building	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	May 01, 2017 $ / shares
Subsequent Event [Line Items]
Payments to acquire real estate			$ 17,099,000	$ 24,289,000
Preferred Stock, Dividend Rate, Percentage			5.875%		5.875%
Acquisition related deposits			$ 500,000		$ 0
Series A Preferred Stock
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage			5.875%
Subsequent Event | Operating Partnership Units
Subsequent Event [Line Items]
Dividends Payable, Amount Per Share | $ / shares						$ 0.145
Subsequent Event | Series A Preferred Stock
Subsequent Event [Line Items]
Dividends Payable, Amount Per Share | $ / shares						0.36719
Subsequent Event | Common Stock
Subsequent Event [Line Items]
Dividends Payable, Amount Per Share | $ / shares						$ 0.145
Subsequent Event | 2930 Ward Avenue
Subsequent Event [Line Items]
Payments to acquire real estate		$ 16,500,000
Number of Buildings | building		1
Rentable square feet | ft²		138,700
Subsequent Event | Archibald Ave
Subsequent Event [Line Items]
Payments to acquire real estate		$ 6,500,000
Subsequent Event | Business Park [Member]
Subsequent Event [Line Items]
Payments to acquire real estate	$ 141,200,000
Rentable square feet | ft²	1,100,000
Acquisition related deposits	$ 4,000,000
Subsequent Event | 2811 Harbor Boulevard
Subsequent Event [Line Items]
Contractual Sales Price		$ 18,700,000