Revenue - Summary of Revenue from Tenant Construction Projects Disaggregated by Tenant Agency (Detail) - ASU 2014-09 [Member] - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Disaggregation Of Revenue [Line Items]
Tenant Construction Project Income	$ 1,602	$ 2,645
Administrative Office of the U.S. Courts ("AOC") [Member]
Disaggregation Of Revenue [Line Items]
Tenant Construction Project Income	12	112
Drug Enforcement Administration ("DEA") [Member]
Disaggregation Of Revenue [Line Items]
Tenant Construction Project Income	163	186
Federal Bureau of Investigation ("FBI") [Member]
Disaggregation Of Revenue [Line Items]
Tenant Construction Project Income	67	125
Immigration and Customs Enforcement ("ICE") [Member]
Disaggregation Of Revenue [Line Items]
Tenant Construction Project Income		9
National Park Service ("NPS") [Member]
Disaggregation Of Revenue [Line Items]
Tenant Construction Project Income		31
Social Security Administration ("SSA") [Member]
Disaggregation Of Revenue [Line Items]
Tenant Construction Project Income	14	14
U.S. Coast Guard ("USCG") [Member]
Disaggregation Of Revenue [Line Items]
Tenant Construction Project Income		6
U.S. Citizenship and Immigration Services ("USCIS") [Member]
Disaggregation Of Revenue [Line Items]
Tenant Construction Project Income	39	39
U.S. Forest Service ("USFS") [Member]
Disaggregation Of Revenue [Line Items]
Tenant Construction Project Income	61	90
Department of Veteran Affairs ("VA") [Member]
Disaggregation Of Revenue [Line Items]
Tenant Construction Project Income	$ 1,246	$ 2,033