Share-based payments (Tables)

3 Months Ended

Mar. 31, 2021

Share-based payments

Compensation Costs Related to Share-Based Payments

	Three months ended
	March 31,
	2021		2020
SG&A expenses:
Stock option compensation expense	$	1,861	$	1,187
Equity-classified share units		3,153		1,786
Liability-classified share units		(1,915)		(1,156)
Employee share purchase plan - employer contributions		679		590
		3,778		2,407
Acquisition-related costs:
Share-based continuing employment costs		2,553		—
		2,553		—
	$	6,331	$	2,407

Summary of Stock Option Activity

				WA
	Common	WA		remaining		Aggregate
	shares under	exercise		contractual		intrinsic
	option	price		life (in years)		value
Outstanding, December 31, 2020	1,985,754	$	34.95		7.7	$	68,717
Granted	684,761		54.83
Exercised	(197,863)		33.96				4,538
Forfeited	(6,533)		35.39
Outstanding, March 31, 2021	2,466,119		40.54		8.0		44,460
Exercisable, March 31, 2021	1,046,861	$	31.27		6.3	$	28,557

Summary of Significant Assumptions Used to Estimate the Fair Value of Stock Options

Three months ended March 31,	2021		2020
Risk free interest rate	0.5	%	0.8	%
Expected dividend yield	1.66	%	2.02	%
Expected lives of the stock options	4	years	5	years
Expected volatility	32.3	%	27.3	%

Summary of Share Unit Activity

	Equity-classified awards						Liability-classified awards
	PSUs			RSUs			DSUs
		WA grant			WA grant				WA grant
		date fair			date fair				date fair
	Number	value		Number	value			Number	value
Outstanding, December 31, 2020	542,676	$	38.09	134,937	$	39.14	$	137,514	$	32.06
Granted	137,848		56.81	28,560		56.45		4,525		52.08
Vested and settled	(161,248)		31.14	(87,409)		33.14		—		—
Forfeited	(10,750)		48.54	(4,089)		64.32		—		—
Outstanding, March 31, 2021	508,526	$	45.14	71,999	$	51.87	$	142,039	$	32.70