Share-based payments consist of the following compensation costs:


Year ended December 31,	2019		2018		2017
Stock option compensation expense:
SG&A expenses	$	4,697	$	7,895	$	8,948
Acquisition-related costs		—		357		4,752
Share unit expense:
Equity-classified share units		8,047		11,256		3,529
Liability-classified share units		1,380		1,764		670
Employee share purchase plan - employer contributions		2,281		2,174		1,813
	$	16,405	$	23,446	$	19,712

Share unit activity for the years ended December 31, 2019, 2018, and 2017 is presented below:


	Equity-classified awards						Liability-classified awards
	PSUs			RSUs			PSUs⁽¹⁾			RSUs			DSUs
		WA grant			WA grant			WA grant			WA grant			WA grant
		date fair			date fair			date fair			date fair			date fair
	Number	value		Number	value		Number	value		Number	value		Number	value
Outstanding, December 31, 2016	243,968	$	27.48	—	$	—	311,329	$	23.96	160,009	$	23.37	73,520	$	25.41
Granted	136,073		30.28	125,152		26.93	98,775		31.21	878		32.30	19,967		29.67
Transferred to (from) equity awards on modification	81,533		24.47	—		—	(81,533)		24.66	—		—	—		—
Vested and settled	(27,326)		26.82	—		—	(49,873)		23.64	(156,221)		23.33	—		—
Forfeited	—		—	—		—	(19,457)		26.39	—		—	—		—

Outstanding, December 31, 2017	434,248	$	27.83	125,152	$	26.93	259,241	$	26.38	4,666	$	26.42	93,487	$	26.32
Granted	240,803		35.63	91,251		32.10	—		—	66		34.70	26,553		33.42
Transferred to equity awards on modification	257,659		31.30	—		—	(257,659)		26.38	—		—	—		—
Vested and settled	(212,263)		33.78	—		—	—		—	(4,732)		26.54	(6,605)		23.16
Forfeited	(50,159)		31.41	(8,417)		32.00	(1,582)		26.45	—		—	—		—
Outstanding, December 31, 2018	670,288	$	31.46	207,986	$	28.99	—	$	—	—	$	—	113,435	$	28.16
Granted	170,208		36.13	36,350		35.40	—		—	—		—	24,810		35.99
Vested and settled	(251,883)		30.33	(265)		31.98	—		—	—		—	(19,877)		27.45
Forfeited	(159,889)		33.21	(6,651)		34.27	—		—	—		—	—		—
Outstanding, December 31, 2019	428,724	$	32.89	237,420	$	29.72	—	$	—	—	$	—	118,368	$	29.64

(1)	Liability-classified PSUs include PSUs awarded under the employee PSU plan and the previous 2013 PSU plan, in place prior to 2015, are cash-settled and not subject to market vesting conditions.


Year ended December 31,	2017
Risk free interest rate	1.5	%
Expected dividend yield	2.01	%
Expected lives of the PSUs	3	years
Expected volatility	28.9	%
Average expected volatility of comparable companies	33.4	%


Year ended December 31,	2017
Risk free interest rate	0.8	%
Expected dividend yield	2.19	%
Expected lives of the stock options	0.4	years
Expected volatility	32.1	%