Leases - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Leases [Abstract]
Lease payments to be made on leases not yet commenced	$ 40.9	$ 40.9

Lessee, Operating Lease, Lease Not Yet Commenced, Undiscounted Amount

No definition available.

Name:	kvsb_LesseeOperatingLeaseLeaseNotYetCommencedUndiscountedAmount
Namespace Prefix:	kvsb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant