Concentrations Risk - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2020 Property
Wholly Owned Properties [Member]
Concentration Risk [Line Items]
Number of properties	72
California [Member]
Concentration Risk [Line Items]
Number of properties	18
Lease Income [Member] | Credit Concentration Risk [Member] | California [Member]
Concentration Risk [Line Items]
Percentage of concentrations risk	26.30%
Rentable Square Feet [Member] | Credit Concentration Risk [Member] | California [Member]
Concentration Risk [Line Items]
Percentage of concentrations risk	19.70%
U.S. Government [Member] | Lease Income [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage of concentrations risk	98.30%
Non Governmental Tenants [Member] | Lease Income [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage of concentrations risk	1.70%