Commitments and Contingencies - Additional Information (Detail)	1 Months Ended	6 Months Ended	9 Months Ended
	May 31, 2018 ft² yr	Jun. 30, 2018 ft²	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Indemnification Obligation [Member]
Loss Contingencies [Line Items]
Litigation matters, liabilities | $			$ 0	$ 0
Kilroy Realty Finance Partnership, L.P [Member]
Loss Contingencies [Line Items]
Lease space | ft²	135,936
Leased space delivered | ft²		1,726
Lease term start year	2018
Lease expiration year	2030
Remaining square feet of space expected delivery period	fourth quarter of 2018
Remaining square feet of space expected delivery year	2019
Lease expiration date	Jan. 31, 2030
Lease, option to extend, description	The lease term will end on January 31, 2030, subject to our right to extend the term of the Lease for a consecutive five-year period.
Number of consecutive 5 year terms to extend lease | yr	1
Lease extension term	5 years
Annual base rent of operating lease | $			$ 10,900,000
Operating lease, annual rate of increase in rent			3.00%