Employee Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Tax Deferred Savings Plan [Abstract]
Employee Deferral Percent for 401(k)	100.00%upl_EmployeeDeferralPercent
Company Matching Percent for 401(k)	5.00%upl_CompanyMatchPercent
Company Discretionary Contribution for 401(k)	8.00%upl_DiscretionaryContribution
Pension and Other Postretirement Benefit Contributions [Abstract]
Other Postretirement Benefits Payments	$ 2.0	$ 1.6	$ 1.8

The Company's matching percentage of an employee's contribution up to 5% of compensation in accordance with the Company sponsored, qualified, tax-deferred savings plan in accordance with provisions of Section 401(k) of the Internal Revenue Code.

No definition available.

+ Details

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- Definition

The Company's discretionary contribution percentage of compensation in accordance with the Company sponsored, qualified, tax-deferred savings plan in accordance with provisions of Section 401(k) of the Internal Revenue Code.

+ References

No definition available.

+ Details

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- Definition

Percentage of an employee's compensation that may be deferred in accordance with the Company sponsored, qualified, tax-deferred savings plan in accordance with provisions of Section 401(k) of the Internal Revenue Code.

+ References

No definition available.

+ Details

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- Details

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- Definition

The amount of cash or cash equivalents contributed during the reporting period by the entity to fund non-pension postretirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

+ Details

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- Details

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