Stock Based Compensation - Status of United's Nonvested Stock Option Awards (Detail)	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares, Nonvested, Beginning balance | shares	589,737
Shares, Granted | shares	183,551
Shares, Vested | shares	(225,132)
Shares, Forfeited or expired | shares	(2,351)
Shares, Nonvested, Ending balance | shares	545,805
Weighted-Average Grant Date Fair Value Per Share, Nonvested Beginning balance | $ / shares	$ 7.62
Weighted-Average Grant Date Fair Value Per Share, Granted | $ / shares	5.65
Weighted-Average Grant Date Fair Value Per Share, Vested | $ / shares	7.68
Weighted-Average Grant Date Fair Value Per Share, Forfeited or expired | $ / shares	7.32
Weighted-Average Grant Date Fair Value Per Share, Nonvested Ending balance | $ / shares	$ 6.94