Concentrations Risk - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2015 Property
Wholly Owned Properties [Member]
Concentration Risk [Line Items]
Number of properties	36
California [Member]
Concentration Risk [Line Items]
Number of properties	13
Lease Income [Member] | Credit Concentration Risk [Member] | California [Member]
Concentration Risk [Line Items]
Percentage of concentrations risk	31.80%
Rentable Square Feet [Member] | Credit Concentration Risk [Member] | California [Member]
Concentration Risk [Line Items]
Percentage of concentrations risk	23.60%
General Services Administration And Other Federal Agencies [Member] | Lease Income [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage of concentrations risk	96.20%
Non Governmental Tenants [Member] | Lease Income [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage of concentrations risk	3.80%