Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Liability of unrecognized tax benefits	$ 2,198
Estimate of unrecognized tax benefits, reasonable possible	United cannot reasonably estimate the amount of tax benefits it may recognize over the next 12 months.
Accrued interest related to uncertain tax positions	$ 792	$ 548

No definition available.

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- Definition

A statement that a range of reasonably possible change cannot be made for a tax position taken for which it is reasonably possible that the total amount of unrecognized tax benefit will significantly increase or decrease within 12 months of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (d)(3)
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32718-109319

+ Details

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- Definition

Amount of interest expense accrued for an underpayment of income taxes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32718-109319

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- Definition

The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65882285&loc=SL6600010-109319

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