Stock Based Compensation - Status of United's Nonvested Stock Option Awards (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Nonvested, Beginning balance	770,750
Shares, Granted	194,225
Shares, Vested	348,339
Shares, Forfeited or expired	27,439
Shares, Nonvested, Ending balance	589,197
Weighted-Average Grant Date Fair Value Per Share, Nonvested beginning Balance	$ 7.04
Weighted-Average Grant Date Fair Value Per Share, Granted	$ 5.74
Weighted-Average Grant Date Fair Value Per Share, Vested	$ 6.33
Weighted-Average Grant Date Fair Value Per Share, Forfeited or expired	$ 7.53
Weighted-Average Grant Date Fair Value Per Share, Nonvested Ending balance	$ 7.01