Subsequent Events (Detail)						3 Months Ended	6 Months Ended		12 Months Ended
	Jul. 28, 2017 USD ($) ft² building	Jul. 20, 2017 USD ($) ft² building	Jul. 18, 2017 USD ($) ft² building	Jul. 11, 2017 USD ($) ft² building	Jul. 03, 2017 USD ($) ft² building	Jun. 30, 2017 USD ($) ft²	Jun. 30, 2017 USD ($) ft² building	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Jul. 31, 2017 $ / shares	Jul. 13, 2017 USD ($)
Subsequent Event [Line Items]
Payments to acquire real estate							$ 240,447,000	$ 228,131,000
Rentable square feet | ft²						1,764,112	1,764,112
Principal amount						$ 564,242,000	$ 564,242,000		$ 502,476,000
Number of Buildings | building							23
Preferred Stock, Dividend Rate, Percentage						5.875%			5.875%
Series A Preferred Stock
Subsequent Event [Line Items]
Preferred Stock, Dividend Rate, Percentage						5.875%
Subsequent Event
Subsequent Event [Line Items]
Prepayment of principal minimum amount											$ 2,500,000
Principal Prepayment Percentage											100.00%
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 | 4832 Azusa Canyon Road [Member]
Subsequent Event [Line Items]
Payments to acquire real estate	$ 14,600,000
Rentable square feet | ft²	87,421
Number of Buildings | building	1
Subsequent Event | 11190 White Birch Drive [Member]
Subsequent Event [Line Items]
Payments to acquire real estate		$ 19,800,000
Rentable square feet | ft²		201,035
Number of Buildings | building		1
Subsequent Event | 3002-3072 Inland Empire Boulevard [Member]
Subsequent Event [Line Items]
Payments to acquire real estate					$ 26,900,000
Rentable square feet | ft²					218,407
Number of Buildings | building					4
Subsequent Event | 17000 Kingsview Avenue and 800 Sandhill Avenue [Member]
Subsequent Event [Line Items]
Payments to acquire real estate				$ 14,000,000
Rentable square feet | ft²				100,121
Number of Buildings | building				1
Subsequent Event | Rancho Pacifica Industrial Park [Member]
Subsequent Event [Line Items]
Payments to acquire real estate			$ 210,500,000
Rentable square feet | ft²			1,200,000
Number of Buildings | building			6
$125M senior notes [Member]
Subsequent Event [Line Items]
Principal amount						$ 125,000,000.0	$ 125,000,000.0
$125M senior notes [Member] | Subsequent Event
Subsequent Event [Line Items]
Principal amount											$ 125,000,000.0
Stated Interest Rate											3.93%
Guaranteed Senior Notes
Subsequent Event [Line Items]
Principal amount						$ 100,000,000	$ 100,000,000		$ 100,000,000
Stated Interest Rate						4.29%	4.29%