Employee Benefits - Summary of Equity-Based Awards for Employees (Detail)	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Common Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested common stock awards, Beginning balance | shares	152,882
Granted | shares	7,420
Vested | shares	(568)
Forfeited/Cancelled | shares	(1,759)
Nonvested common stock awards, Ending balance | shares	157,975
Nonvested performance-based stock awards, Beginning balance | $ / shares	$ 52.93
Granted | $ / shares	75.88
Vested | $ / shares	52.63
Forfeited/Cancelled | $ / shares	52.25
Nonvested performance-based stock awards, Ending balance | $ / shares	$ 54.02
Performance Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested performance-based stock awards/units, Beginning balance | shares	160,289
Granted | shares	57,450
Vested | shares	0
Forfeited/Cancelled | shares	0
Nonvested performance-based stock awards/units, Ending balance | shares	217,739
Nonvested performance-based stock awards/units, Beginning balance | $ / shares	$ 50.49
Granted | $ / shares	77.28
Vested | $ / shares	0
Forfeited/Cancelled | $ / shares	0
Nonvested performance-based stock awards/units, Ending balance | $ / shares	$ 57.53
Performance Based Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested performance-based stock awards/units, Beginning balance | shares	13,186
Granted | shares	0
Vested | shares	0
Forfeited/Cancelled | shares	(92)
Nonvested performance-based stock awards/units, Ending balance | shares	13,094
Nonvested performance-based stock awards/units, Beginning balance | $ / shares	$ 51.62
Granted | $ / shares	0
Vested | $ / shares	0
Forfeited/Cancelled | $ / shares	51.62
Nonvested performance-based stock awards/units, Ending balance | $ / shares	$ 51.62