STOCK-BASED COMPENSATION

3 Months Ended

Mar. 31, 2019

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-based compensation expense related to awards issued under the Company's incentive compensation plans for the three months ended March 31, 2019 and 2018 was as follows (in millions):



	Three Months Ended March 31,
	2019		2018
Cost of sales	$	4.0	$	3.0
Selling, general, and administrative expenses	12.7		11.8
Research and development expenses	4.1		3.6
Total stock-based compensation expense	$	20.8	$	18.4

At March 31, 2019, the total remaining compensation cost related to nonvested stock options, restricted stock units, market-based restricted stock units, performance-based restricted stock units, and employee stock purchase plan ("ESPP") subscription awards amounted to $110.4 million, which will be amortized on a straight-line basis over the weighted-average remaining requisite service period of 29 months.

Fair Value Disclosures

The following table includes the weighted-average grant-date fair values of stock options granted during the periods indicated and the related weighted-average assumptions used in the Black-Scholes option pricing model:



Option Awards	Three Months Ended March 31,
	2019			2018
Average risk-free interest rate	2.5		%	2.6		%
Expected dividend yield	None			None
Expected volatility	29.2		%	33.2		%
Expected term (years)	5.2			4.7
Fair value, per option	$	54.03		$	43.45

The following table includes the weighted-average grant-date fair values for ESPP subscriptions granted during the periods indicated and the related weighted-average assumptions used in the Black-Scholes option pricing model:



ESPP	Three Months Ended March 31,
	2019			2018
Average risk-free interest rate	2.4		%	1.5		%
Expected dividend yield	None			None
Expected volatility	32.6		%	32.6		%
Expected term (years)	0.6			0.6
Fair value, per share	$	48.83		$	35.07