Leases - Additional Information (Detail) $ in Thousands	1 Months Ended		9 Months Ended
	Dec. 31, 2018 ft² space	Aug. 31, 2017 ft² extension_period	Sep. 30, 2019 USD ($) ft²	Sep. 30, 2018 USD ($)	Aug. 31, 2019 ft²	Jun. 30, 2018 ft²	May 31, 2018 ft²
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets recognized in exchange for lease liabilities			$ 56,025	$ 0
Cash paid for amounts included in the measurement of lease liabilities			$ 5,100
Operating lease liability, weighted-average remaining lease term			10 years 3 months 18 days
Operating lease liability, weighted-average discount rate, percent			5.90%
ARE-San Francisco No. 19, LLC | Mission Bay Lease
Lessee, Lease, Description [Line Items]
Lease space (in sq. feet) | ft²		145,085	10,729
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) | ft²		8,000
Operating lease right-of-use assets recognized in exchange for lease liabilities			$ 5,000
Kilroy Realty Finance Partnership, L.P | Third Street Lease
Lessee, Lease, Description [Line Items]
Lease space (in sq. feet) | ft²	67,105				67,105	1,726	135,936
Lease extension term							5 years
Operating lease right-of-use assets recognized in exchange for lease liabilities			$ 51,000
Number of additional spaces delivered | space	2