The maximum borrowing capacity that the company may be increased to according to the credit agreement.

No definition available.

Name:	ulbi_LineOfCreditFacilityMaximumBorrowingCapacityMayBeIncreasedTo
Namespace Prefix:	ulbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The minimum fixed charge coverage ratio required for certain debt covenants.

+ References

No definition available.

+ Details

Name:	ulbi_MinimumFixedChargeCoverageRatio
Namespace Prefix:	ulbi_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum tangible net worth of the company required for certain debt covenants.

+ References

No definition available.

+ Details

Name:	ulbi_MinimumTangibleNetWorth
Namespace Prefix:	ulbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=ulbi_KeybankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=ulbi_PNCBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 6 - Debt (Details Textual) $ in Thousands		10 Months Ended	12 Months Ended
Note 6 - Debt (Details Textual) $ in Thousands	May 31, 2017 USD ($)	Apr. 01, 2018	Dec. 31, 2017 USD ($)
KeyBank [Member] \| Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 30,000
Line of Credit Facility Maximum Borrowing Capacity May Be Increased to	50,000
Long-term Line of Credit			$ 0
Minimum Fixed Charge Coverage Ratio			1.15
Minimum Tangible Net Worth			$ 40,000
Letters of Credit Outstanding, Amount			0
KeyBank [Member] \| Revolving Credit Facility [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Scenario, Forecast [Member]
Debt Instrument, Basis Spread on Variable Rate		1.85%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.20%
KeyBank [Member] \| Revolving Credit Facility [Member] \| Base Rate [Member] \| Scenario, Forecast [Member]
Debt Instrument, Basis Spread on Variable Rate		(0.50%)
KeyBank [Member] \| Letter of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,500
PNC Bank [Member] \| Revolving Credit Facility [Member]
Long-term Line of Credit			$ 0