Stock-based compensation plans (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Restricted Stock and Restricted Stock Unit Activity

A summary of restricted stock and restricted stock unit activity follows:

	Restricted Stock Units Outstanding			Weighted- Average Grant Price		Restricted Stock Outstanding			Weighted- Average Grant Price
Unvested at January 1, 2020		691,227		$	171.72		63,591		$	162.45
Granted		480,949			168.71		—			—
Vested		(334,795	)		172.56		(49,468	)		162.48
Cancelled		(20,431	)		171.91		(573	)		158.02
Unvested at December 31, 2020		816,950		$	169.60		13,550		$	162.50

Summary of Stock Option Activity

A summary of stock option activity follows:

				Weighted-Average
	Stock Options Outstanding			Exercise Price		Life (In Years)		Aggregate Intrinsic Value (In thousands)
Outstanding at January 1, 2020		305,452		$	170.15
Granted		187,088			173.04
Exercised		(25,047	)		117.81
Expired		(2,070	)		174.09
Outstanding at December 31, 2020		465,423		$	174.11		8.2	$	38
Exercisable at December 31, 2020		133,098		$	178.58		7.4	$	38