Real Estate and Intangibles - Fair Values of Assets Acquired and Liabilities Assumed (Detail) - Operating Properties Acquired [Member] - DEA Sterling, VA, FDA College Park, MD, Various GSA Portland, OR, JSC -Suffolk, and FBI - New Orleans [Member] $ in Thousands	Mar. 31, 2020 USD ($)
Business Acquisition [Line Items]
Total real estate	$ 47,314
Total intangible assets	13,075
Total intangible liabilities	(8,491)
Contingent consideration	(336)
Purchase price	51,562
Real Estate Investment [Member]
Business Acquisition [Line Items]
Land	4,215
Building	38,705
Acquired tenant improvements	4,394
In-place leases [Member]
Business Acquisition [Line Items]
Total intangible assets	4,384
Acquired Leasing Commissions [Member]
Business Acquisition [Line Items]
Total intangible assets	2,138
Above Market Leases [Member]
Business Acquisition [Line Items]
Total intangible assets	6,553
Below Market Leases [Member]
Business Acquisition [Line Items]
Total intangible liabilities	$ (8,491)