Subsequent Events - Summary of Property Portfolio (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
Real Estate Properties [Line Items]
Purchase Price	$ 110,530,000
California | La Verne
Real Estate Properties [Line Items]
Purchase Price	4,120,000
Year Built	1986
Physical Occupancy	86.00%	[1]
California | Chico
Real Estate Properties [Line Items]
Purchase Price	1,780,000
Year Built	1984
Physical Occupancy	89.00%	[1]
California | Riverside
Real Estate Properties [Line Items]
Purchase Price	2,760,000
Year Built	1985
Physical Occupancy	83.00%	[1]
California | Fairfield
Real Estate Properties [Line Items]
Purchase Price	3,880,000
Year Built	1984
Physical Occupancy	91.00%	[1]
California | Lancaster
Real Estate Properties [Line Items]
Purchase Price	1,760,000
Year Built	1980
Physical Occupancy	74.00%	[1]
California | Upland
Real Estate Properties [Line Items]
Purchase Price	6,230,000
Year Built	1979
Physical Occupancy	90.00%	[1]
California | Vallejo
Real Estate Properties [Line Items]
Purchase Price	5,240,000
Year Built	1981
Physical Occupancy	90.00%	[1]
California | Santa Rosa
Real Estate Properties [Line Items]
Purchase Price	10,420,000
Year Built	1979-1981
Physical Occupancy	89.00%	[1]
California | La Habra
Real Estate Properties [Line Items]
Purchase Price	4,560,000
Year Built	1981
Physical Occupancy	82.00%	[1]
California | Santa Ana
Real Estate Properties [Line Items]
Purchase Price	9,230,000
Year Built	1978
Physical Occupancy	83.00%	[1]
California | Huntington Beach
Real Estate Properties [Line Items]
Purchase Price	10,830,000
Year Built	1986
Physical Occupancy	90.00%	[1]
California | Lompoc
Real Estate Properties [Line Items]
Purchase Price	3,990,000
Year Built	1982
Physical Occupancy	91.00%	[1]
California | Monterey Park
Real Estate Properties [Line Items]
Purchase Price	4,380,000
Year Built	1987
Physical Occupancy	87.00%	[1]
California | Whittier
Real Estate Properties [Line Items]
Purchase Price	5,870,000
Year Built	1989
Physical Occupancy	87.00%	[1]
Colorado | Littleton
Real Estate Properties [Line Items]
Purchase Price	4,300,000
Year Built	1985
Physical Occupancy	86.00%	[1]
Colorado | Federal Heights
Real Estate Properties [Line Items]
Purchase Price	4,700,000
Year Built	1983
Physical Occupancy	88.00%	[1]
Colorado | Aurora
Real Estate Properties [Line Items]
Purchase Price	7,290,000
Year Built	1984
Physical Occupancy	87.00%	[1]
Illinois | Crestwood
Real Estate Properties [Line Items]
Purchase Price	2,440,000
Year Built	1987
Physical Occupancy	92.00%	[1]
Illinois | Bloomingdale
Real Estate Properties [Line Items]
Purchase Price	4,950,000
Year Built	1987
Physical Occupancy	85.00%	[1]
Maryland | Forestville
Real Estate Properties [Line Items]
Purchase Price	6,650,000
Year Built	1988
Physical Occupancy	84.00%	[1]
Washington | Everett
Real Estate Properties [Line Items]
Purchase Price	$ 5,150,000
Year Built	1986
Physical Occupancy	82.00%	[1]

[1] Represents the occupied square feet divided by total rentable square feet as of December 31, 2014.