Share Based Compensation - Textuals (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Share Based Compensation Details [Abstract]
Long Term Incentive Program Period	$ 2.3	$ 1.7
Long Term Incentive Program Total 2011 Program	12.2
Long Term Incentive Program Total 2012 Program	12.5
Long Term Incentive Program Total 2013 Program	15.5
Long Term Incentive Program Total 2010 Program	$ 11.7
Long Term Incentive Program Total 2010 Program Shares	153,511

Pretax compensation expense recognized related to the Long Term Incentive Program in the period.

No definition available.

Name:	upl_LongTermIncentiveProgramPeriod
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The actual total compensation for each of the three year performance periods related to the 2010 LTIP.

No definition available.

Name:	upl_LongTermIncentiveProgramTotal2010Program
Namespace Prefix:	upl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Net shares awarded and issued associated with the 2010 Long Term Incentive Program.

No definition available.

Name:	upl_LongTermIncentiveProgramTotal2010ProgramShares
Namespace Prefix:	upl_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

The estimated total compensation for each of the three year performance periods related to the 2011 LTIP.

No definition available.

Name:	upl_LongTermIncentiveProgramTotal2011Program
Namespace Prefix:	upl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The estimated total compensation for each of the three year performance periods related to the 2012 LTIP.

No definition available.

Name:	upl_LongTermIncentiveProgramTotal2012Program
Namespace Prefix:	upl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The estimated total compensation for each of the three year performance periods related to the 2013 LTIP.

No definition available.

Name:	upl_LongTermIncentiveProgramTotal2013Program
Namespace Prefix:	upl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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