Leases - Additional Information (Detail) $ in Millions	1 Months Ended			6 Months Ended
	Dec. 31, 2018 ft² space	May 31, 2018 ft²	Aug. 31, 2017 ft² extension_period	Jun. 30, 2019 USD ($) ft²	Jun. 30, 2018 ft²
Lessee, Lease, Description [Line Items]
Cash paid for amounts included in the measurement of lease liabilities | $				$ 3.1
Operating lease liability, weighted-average remaining lease term				10 years 7 months 6 days
Operating lease liability, weighted-average discount rate, percent				6.50%
ARE-San Francisco No. 19, LLC | Mission Bay Lease
Lessee, Lease, Description [Line Items]
Lease space (in sq. feet)			137,046	2,690
Number of consecutive 5 year terms to extend lease | extension_period			2
Lease extension term			5 years
Additional space required to be leased in the future (in sqft)			15,000
Recognized a right-of-use asset and lease liability | $				$ 1.3
Kilroy Realty Finance Partnership, L.P | Third Street Lease
Lessee, Lease, Description [Line Items]
Lease space (in sq. feet)	67,105	135,936			1,726
Lease extension term		5 years
Lease term start month and year		2018-06
Number of additional spaces delivered | space	2