Stock-Based Compensation (Tables)

The components and classification of stock-based compensation expense were as follows (in thousands):



	Three Months Ended
	April 3, 2020		March 29, 2019
Stock options	$	13	$	101
RSUs	1,725		2,612
Total stock-based compensation expense	$	1,738	$	2,713

Cost of sales	$	454	$	317
Selling, general and administrative expenses	1,136		2,330
Research, development and engineering costs	148		66
Total stock-based compensation expense	$	1,738	$	2,713

The following table summarizes the Company’s stock option activity:



	Number of Stock Options		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (In Years)	Aggregate Intrinsic Value (In Millions)
Outstanding at December 31, 2019	384,013		$	34.96
Exercised	(58,658	)	37.60
Outstanding at April 3, 2020	325,355		$	34.48	5.0	$	5.7
Exercisable at April 3, 2020	322,805		$	34.40	5.0	$	5.6

The weighted average fair value and assumptions used to value the TSR portion of the PRSUs granted are as follows:

The following table summarizes time-vested RSU activity:



	Time-Vested Activity		Weighted Average Grant Date Fair Value
Nonvested at December 31, 2019	205,223		$	64.75
Granted	107,030		85.58
Vested	(64,334	)	54.89
Forfeited	(7,524	)	70.37
Nonvested at April 3, 2020	240,395		$	76.49

The following table summarizes PRSU activity:



	Performance- Vested Activity		Weighted Average Grant Date Fair Value
Nonvested at December 31, 2019	191,592		$	56.30
Granted	66,690		95.15
Vested	(35,363	)	31.17
Forfeited	(4,106	)	51.54
Nonvested at April 3, 2020	218,813		$	72.29