The Company has a 401(k) profit-sharing plan for U.S. employees meeting certain requirements, in which eligible employees may contribute between 1% and 50% of their annual compensation to this plan, and, with respect to employees who are age 50 and older, certain specified additional amounts, limited by an annual maximum amount determined by the Internal Revenue Service. The Company, at its discretion, makes certain matching contributions to this plan based on participating employees’ annual contribution to this plan and their total compensation. The Company’s contributions were $7.2, $6.9 and $6.1 for 2020, 2019 and 2018, respectively.

The Company maintains a bonus plan which provides cash awards to key employees, at the discretion of the Compensation Committee of the Company’s Board of Directors, based upon the Company’s operating results. In addition, the Company’s foreign locations also have various bonus plans based upon local operating results and employee performance. The total bonus expense was $66.4, $32.2 and $38.3 for 2020, 2019 and 2018, respectively.

The Company provides supplemental retirement benefits for a number of retired executives. The total cost of these benefits was $0.3, $3.2 and $4.6 for 2020, 2019 and 2018, respectively. The accumulated benefit obligation was $2.5 and was included in other non-current liabilities at December 31, 2020. The current accumulated benefit obligation was $21.3 and was included in other current liabilities and the non-current accumulated benefit obligation was $2.5 and was included in other non-current liabilities at December 31, 2019. The decrease in the accumulated benefit obligation from 2019 to 2020 was attributed to a large supplemental retirement benefit payment made during 2020 to the Company’s former Chief Executive Officer in connection with his retirement.

The Company also assumed deferred compensation plans as a result of each of the Newport Merger and the ESI Merger. Participants in the Newport DC Plan were not permitted to make any new elections beginning with 2018 compensation. Participants in the ESI DC Plan were not permitted to make any new elections beginning with 2020 compensation.

As a result of the Newport Merger, the Company assumed all assets and liabilities of Newport’s defined benefit pension plans, which cover substantially all of its full-time employees in France, Germany, Israel and Japan. In addition, there are certain pension assets and liabilities relating to its former employees in the United Kingdom. The German plan is unfunded, as permitted under the plan and applicable laws.

As a result of the ESI Merger, the Company assumed all assets and liabilities of ESI’s defined benefit pension plans, which cover substantially all of its full-time employees in Japan, South Korea and Taiwan.

For financial reporting purposes, the calculation of net periodic pension costs was based upon a number of actuarial assumptions including a discount rate for plan obligations, an assumed rate of return on pension plan assets and an assumed

rate of compensation increase for employees covered by the plan. All of these assumptions were based upon management’s judgment, considering all known trends and uncertainties. Actual results that differ from these assumptions would impact future expense recognition and the cash funding requirements of the Company’s pension plans.

	Year Ended December 31,
	2020			2019
Service cost	$	1.0		$	0.8
Interest cost on projected benefit obligations		0.4			0.5
Expected return on plan assets		(0.1	)		(0.1	)
Amortization of actuarial net loss		0.5			0.1
	$	1.8		$	1.3

The changes in projected benefit obligations and plan assets, as well as the ending balance sheet amounts for the Company’s defined benefit plans, were as follows:

	Year Ended December 31,
	2020			2019
Change in projected benefit obligations:
Projected benefit obligations, beginning of year	$	30.1		$	24.9
Assumed in ESI Merger		—			3.5
Service cost		1.0			0.8
Interest cost		0.4			0.5
Contributions by plan participants		0.7			—
Plan amendments		(0.2	)		—
Actuarial loss		3.0			2.1
Benefits paid		(1.2	)		(1.5	)
Currency translation adjustments		2.4			(0.2	)
Projected benefit obligations, end of year	$	36.2		$	30.1

Change in plan assets:
Fair value of plan assets, beginning of year	$	11.1		$	7.8
Assumed in ESI Merger		—			1.3
Company contributions		1.1			1.8
Gain on plan assets		0.6			0.6
Benefits paid		(0.5	)		(0.5	)
Currency translation adjustments		0.6			0.1
Fair value of plan assets, end of year		12.9			11.1
Net underfunded status	$	(23.3	)	$	(19.0	)

As of December 31, 2020, the estimated benefit payments for the Company’s defined benefit plans for the next 10 years were as follows:

The weighted-average rates used to determine the net periodic benefit costs were as follows:

In determining the expected long-term rate of return on plan assets, the Company considers the relative weighting of plan assets, the historical performance of total plan assets and individual asset classes, and economic and other indicators of future performance.

Plan assets were held in the following categories as a percentage of total plan assets:

	December 31, 2020					December 31, 2019
	Amount		Percentage			Amount		Percentage
Cash	$	0.2		1.3	%	$	0.4		3.9	%
Debt securities		5.2	40.5				8.1		72.3
Equity securities		0.7	5.6				1.5		13.7
Other		6.8	52.6				1.1		10.1
	$	12.9		100	%	$	11.1		100	%

In general, the Company’s asset management objectives include maintaining an adequate level of diversification to reduce interest rate and market risk, while providing adequate liquidity to meet immediate and future benefit payment requirements.

The Company’s Israeli plans account for the deferred vested benefits using the shut-down method of accounting, which resulted in assets of $18.8 and vested benefit obligations of $21.7 as of December 31, 2020 and assets of $16.7 and vested benefit obligations of $19.7 as of December 31, 2019. Under the shut-down method, the liability is calculated as if it were payable as of the balance sheet date, on an undiscounted basis.

As of December 31, 2020 and 2019, the Company had assets with an aggregate market value of $6.5 and $5.8, respectively, for its German pension plans. These assets are invested in group insurance contracts through the insurance companies administering these plans, in accordance with applicable pension laws. These group insurance contracts have a guaranteed minimum rate of return ranging from 2.25% to 4.25%, depending on the contract. Because these assets were not separate legal assets of the pension plan, they were not included in the Company’s plan assets shown above. However, the Company has designated such assets to pay pension benefits. Such assets are included in other assets in the accompanying consolidated balance sheet.