Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Summary of Significant Accounting Policies

Estimated useful lives of property, plant and equipment

	Estimated Useful Life
Buildings	25 to 40 years
Machinery and equipment	3 to 10 years
Computer equipment and software	3 to 5 years
Furniture and fixtures	3 to 10 years
Leasehold improvements	Lesser of 15 years or the remaining lease term

Estimated useful lives of finite intangible assets

	Estimated Useful Life
Existing technology and related patents	3 to 15 years
Customer and distributor relationships	5 to 15 years
Trade names	5 to 15 years

Stock-based compensation expense, cost allocation

The following presents the impact of stock-based compensation expense on our consolidated statements of income (in millions):

	2020		2019		2018
Stock options	$	1.8	$	2.7	$	4.2
Restricted stock awards		—		0.3		0.8
Restricted stock units		11.5		8.9		6.3
Total stock-based compensation	$	13.3	$	11.9	$	11.3

	2020		2019		2018
Costs of product revenue	$	2.0	$	1.8	$	1.7
Selling, general and administrative		9.3		8.3		7.9
Research and development		2.0		1.8		1.7
Total stock-based compensation	$	13.3	$	11.9	$	11.3

Assumptions regarding volatility, expected life, dividend yield and risk-free interest rates

Assumptions regarding volatility, expected term, dividend yield and risk-free interest rates are required for the Black-Scholes model and are presented in the table below:

	2020			2019			2018
Risk-free interest rates		0.23	%		1.55	%		2.80	%
Expected life		5.1	years		5.3	years		5.4	years
Volatility		34.1	%		29.57	%		28.46	%
Expected dividend yield		0.37	%		0.38	%		0.47	%
Weighted-average fair value per share	$	12.08		$	11.16		$	9.50