Leases - Additional Information (Detail) $ in Millions	1 Months Ended			3 Months Ended
	Dec. 31, 2018 ft² Space	May 31, 2018 ft²	Aug. 31, 2017 ft² yr	Mar. 31, 2019 USD ($) ft²	Jun. 30, 2018 ft²
Lessee Lease Description [Line Items]
Cash paid for amounts included in the measurement of lease liabilities | $				$ 1.8
Operating lease liability, weighted-average remaining lease term				10 years 9 months 18 days
Operating lease liability, weighted-average discount rate, percent				6.50%
Other Current Assets [Member]
Lessee Lease Description [Line Items]
Additional operating lease incentive | $				$ 4.1
ARE-San Francisco No. 19, LLC [Member] | Mission Bay Lease [Member]
Lessee Lease Description [Line Items]
Extended lease term start year			2020
Lease expiration year			2030
Lease space | ft²			137,046	2,690
Lease commencement date			Sep. 01, 2017
Lessee operating lease, lease expiration date			Jan. 31, 2030
Lease, option to extend, description				The term of the Mission Bay Lease commenced on September 1, 2017, and will expire January 31, 2030, subject to our right to extend the term of the lease for two consecutive five-year periods, which we have excluded from our determination of the lease term.
Number of consecutive 5 year terms to extend lease | yr			2
Lease extension term			5 years
Additional space required to be leased in the future | ft²			15,000
Recognized a right-of-use asset and lease liability | $				$ 1.3
Kilroy Realty Finance Partnership, L.P [Member] | Third Street Lease [Member]
Lessee Lease Description [Line Items]
Lease space | ft²	67,105	135,936			1,726
Lessee operating lease, lease expiration date		Jan. 31, 2030
Lease, option to extend, description				our right to extend the term for a consecutive five-year period
Lease extension term		5 years
Lease term start month and year		2018-06
Number of additional spaces delivered | Space	2
Remaining square feet of space expected delivery year		2019