Stock Based Compensation - Status of United's Nonvested Stock Option Awards (Detail)	6 Months Ended
	Jun. 30, 2022 $ / shares shares
Shares, Nonvested, Beginning balance | shares	395,034
Shares, Granted | shares	0
Shares, Vested | shares	(215,926)
Shares, Forfeited or expired | shares	(8,216)
Shares, Nonvested, Ending balance | shares	170,892
Weighted-Average Grant Date Fair Value Per Share, Nonvested Beginning balance | $ / shares	$ 7.33
Weighted-Average Grant Date Fair Value Per Share, Granted | $ / shares	0
Weighted-Average Grant Date Fair Value Per Share, Vested | $ / shares	8.11
Weighted-Average Grant Date Fair Value Per Share, Forfeited or expired | $ / shares	11.06
Weighted-Average Grant Date Fair Value Per Share, Nonvested Ending balance | $ / shares	$ 6.16
Restricted Stock Units (RSUs) [Member]
Shares, Nonvested, Beginning balance | shares	136,896
Shares, Granted | shares	147,511
Shares, Vested | shares	(18,248)
Shares, Forfeited or expired | shares	0
Shares, Nonvested, Ending balance | shares	266,159
Weighted-Average Grant Date Fair Value Per Share, Nonvested Beginning balance | $ / shares	$ 35.65
Weighted-Average Grant Date Fair Value Per Share, Granted | $ / shares	35.46
Weighted-Average Grant Date Fair Value Per Share, Vested | $ / shares	37.05
Weighted-Average Grant Date Fair Value Per Share, Forfeited or expired | $ / shares	0
Weighted-Average Grant Date Fair Value Per Share, Nonvested Ending balance | $ / shares	$ 35.45