Share-based payments (Tables)

6 Months Ended

Jun. 30, 2021

Share-based payments

Compensation Costs Related to Share-Based Payments

	Three months ended				Six months ended
	June 30,				June 30,
	2021		2020		2021		2020
SG&A expenses:
Stock option compensation expense	$	1,909	$	1,543	$	3,770	$	2,730
Equity-classified share units		4,404		3,231		7,557		5,017
Liability-classified share units		526		971		(1,389)		(185)
Employee share purchase plan - employer contributions		701		610		1,380		1,199
		7,540		6,355		11,318		8,761
Acquisition-related costs:
Share-based continuing employment costs		2,678		—		5,231		—
		2,678		—		5,231		—
	$	10,218	$	6,355	$	16,549	$	8,761

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	690,353		54.88
Exercised	(311,153)		34.38				7,623
Forfeited	(23,808)		46.88
Outstanding, June 30, 2021	2,341,146		40.78		7.9		43,379
Exercisable, June 30, 2021	980,404	$	31.33		6.3	$	27,402

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

Six months ended June 30,	2021		2020
Risk free interest rate	0.5	%	0.7	%
Expected dividend yield	1.66	%	1.98	%
Expected lives of the stock options	4	years	5	years
Expected volatility	32.3	%	27.8	%

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	140,455		56.69	29,525		56.59		9,362		56.33
Vested and settled	(161,248)		31.14	(88,157)		33.20		—		—
Forfeited	(13,765)		48.33	(5,357)		60.16		—		—
Outstanding, June 30, 2021	508,118	$	45.16	70,948	$	52.21		146,876	$	33.61