LEASES - Additional Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) numberOfLeases	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) numberOfLeases	Sep. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Apr. 30, 2019
Lessee, Lease, Description [Line Items]
Remeasurement adjustment					$ 7,500
ROU asset	$ 26,307		$ 26,307
Lease liability	28,720		28,720
Lease incentive receivable	6,884		6,884
Future minimum lease payments	46,734		46,734
Operating lease expense	$ 700	$ 700	$ 500	$ 1,800
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent		us-gaap:OtherAssetsNoncurrent
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent		us-gaap:OtherLiabilitiesCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent		us-gaap:OtherLiabilitiesNoncurrent
Kilroy Realty, L.P.
Lessee, Lease, Description [Line Items]
Number of operating leases | numberOfLeases	2		2
New Office Lease 2020
Lessee, Lease, Description [Line Items]
ROU asset	$ 25,700		$ 25,700		8,900
Lease liability	25,700		25,700		8,800
Lease incentive receivable	5,900		5,900		$ 2,000
Remaining lease term						7 years 7 months
Operating lease extension term						5 years
Future minimum lease payments	49,500		49,500
Lease Space Delivered June 2020
Lessee, Lease, Description [Line Items]
Future minimum lease payments	13,000		13,000
Lease Space Delivered September 2020
Lessee, Lease, Description [Line Items]
Future minimum lease payments	$ 36,500		$ 36,500