Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Stock-based compensation expense consisted of the following:


	Year Ended December 31,
(in thousands)	2019		2018		2017
Cost of sales	$	278	$	250	$	243
SG&A expense	17,554		14,041		11,043
Pre-tax stock-based compensation expense	17,832		14,291		11,286
Income tax benefits	(4,009)		(3,218)		(1,778)
Total stock-based compensation expense, net of tax	$	13,823	$	11,073	$	9,508

The following table presents the weighted average assumptions for stock options granted and resulting fair value in the years ended December 31:


	2019	2018	2017
Expected option term	4.50 years	4.50 years	4.54 years
Expected stock price volatility	27.14%	28.39%	28.91%
Risk-free interest rate	2.49%	2.47%	1.73%
Expected annual dividend yield	1.03%	1.15%	1.29%
Weighted average grant date fair value per share	$22.51	$18.86	$13.11

The following table summarizes stock option activity under the Plan:


	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic Value ⁽¹⁾ (in thousands)
Options outstanding at January 1, 2017	2,151,542	$	37.40	6.39	$	45,253
Granted	540,537	55.90
Cancelled	(246,450)	50.62
Exercised	(675,742)	29.52
Options outstanding at December 31, 2017	1,769,887	44.22		6.69	48,962
Granted	402,010	76.48
Cancelled	(67,440)	60.75
Exercised	(499,836)	36.98
Options outstanding at December 31, 2018	1,604,621	53.86		6.95	48,703
Granted	395,653	93.98
Cancelled	(68,275)	74.10
Exercised	(452,325)	43.76
Options outstanding at December 31, 2019	1,479,674	$	66.74	7.11	$	49,930
Options vested and expected to vest at December 31, 2019	1,421,269	$	66.05	7.05	$	48,915
Options exercisable at December 31, 2019	605,469	$	50.57	5.48	$	30,048

The following table presents the weighted average assumptions for restricted stock units granted in the years ended December 31:


	2019	2018	2017
Vesting period	3.76 years	3.77 years	3.87 years
Expected annual dividend yield	0.97%	1.15%	1.30%
Weighted average grant date fair value per restricted stock unit granted	$94.58	$73.74	$52.45

The following table summarizes the restricted stock unit activity under the Plan:


	Number of Shares	Weighted Average Grant Date Fair Value Per Share
Restricted stock units outstanding at January 1, 2017	466,475	$	47.23
Granted	270,169	52.45
Vested⁽¹⁾	(176,654)	42.32
Forfeited	(110,515)	48.13
Restricted stock units outstanding at December 31, 2017	449,475	52.07
Granted	197,299	73.74
Vested⁽¹⁾	(155,847)	50.97
Forfeited	(66,926)	53.19
Restricted stock units outstanding at December 31, 2018	424,001	62.38
Granted	177,618	94.58
Vested⁽¹⁾	(163,195)	60.45
Forfeited	(33,320)	72.35
Restricted stock units outstanding at December 31, 2019	405,104	$	76.45