Employee Benefits - Information Relating to Non-qualified Option Activity (Detail) - Long-Term Incentive Compensation Plan (LTIP) [Member]	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares
Number of Shares
Outstanding, Beginning Balance | shares	643,319
Canceled | shares	(1,632)
Expired | shares	(14,620)
Exercised | shares	(99,126)
Outstanding, Ending Balance | shares	527,941
Exercisable | shares	501,826
Weighted Average Price Per Share
Outstanding, Beginning Balance | $ / shares	$ 53.72
Canceled | $ / shares	75.25
Expired | $ / shares	60.88
Exercised | $ / shares	46.11
Outstanding, Ending Balance | $ / shares	54.89
Exercisable | $ / shares	$ 53.83
Weighted Average Remaining Contractual Term
Outstanding	4 years
Exercisable	3 years 10 months 24 days
Aggregate Intrinsic Value
Outstanding | $	$ 7,446,101
Exercisable | $	$ 7,609,581