Summary of Significant Accounting Policies - Global Wells (Details) - Global Wells $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Variable Interest Entity [Line Items]
Ownership interest (as a percent)	13.50%
Voting interest (as a percent)	25.00%
Minimum bank account to make additional contributions from members	$ 50
Contributions to offset the amount that member cannot contribute (up to)	$ 25

Represents the contributions to offset the amount that member cannot contribute.

No definition available.

Name:	krt_ContributionsToOffsetAmountThatMemberCannotContribute
Namespace Prefix:	krt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the minimum bank account to make additional contributions from members.

+ References

No definition available.

+ Details

Name:	krt_MinimumBankAccountToMakeAdditionalContributionsFromMembers
Namespace Prefix:	krt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of the Variable Interest Entity's voting interest owned by (or beneficial interest in) the reporting entity.

+ References

No definition available.

+ Details

Name:	krt_VariableInterestEntityQualitativeOrQuantitativeInformationVotingPercentage
Namespace Prefix:	krt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_VariableInterestEntityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=123419778&loc=SL6759159-111685

+ Details

Name:	us-gaap_VariableInterestEntityOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_ConsolidatedEntitiesAxis=krt_GlobalWellsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: