Information by Geography (Narrative) (Detail)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting [Abstract]
Percentage of foreign operations total revenue	5.00%	5.00%	5.00%
Long lived assets of foreign operations	5.00%	5.00%

Percentage of Long-lived assets other than financial instruments, long-term customer relationships of a financial institution, mortgage and other servicing rights, deferred policy acquisition costs, and deferred tax assets.

No definition available.

Name:	knx_Longlivedassetsofforeignoperations
Namespace Prefix:	knx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant