Stock-based compensation plans (Tables)

12 Months Ended

Dec. 31, 2019

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, 2019		556,875		$	170.07		179,439		$	144.18
Granted		448,487			164.63		—			—
Vested		(298,243	)		157.90		(113,894	)		133.69
Cancelled		(15,892	)		173.48		(1,954	)		161.42
Unvested at December 31, 2019		691,227		$	171.72		63,591		$	162.45

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, 2019		220,591		$	157.98
Granted		164,244			164.54
Exercised		(76,181	)		122.55
Expired		(3,202	)		176.41
Outstanding at December 31, 2019		305,452		$	170.15		8.0	$	2,301
Exercisable at December 31, 2019		66,076		$	159.96		5.1	$	1,454