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 these plans based on participating employees’

annual contribution

to the plans and their total compensation. The Company’s contributions were $6,944, $6,093 and $5,651 for 2019, 2018 and 2017, respectively.

The Company maintains a bonus plan which provides cash awards to key employees, at the discretion of the compensation committee of the 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 $32,172, $38,254 and $46,783 for 2019, 2018 and 2017, respectively.

The Company provides supplemental retirement benefits for a number of former retired executives. The total cost of these benefits

was $3,211, $4,609 and $3,478 for 2019, 2018 and 2017, respectively.

The current accumulated benefit obligation

was $21,341 and

was included in other current liabilities and the

non-current

accumulated benefit obligation was $2,471 and was included in other

non-current

liabilities at December 31, 2019. The accumulated benefit obligation

was $20,644 at December 31, 2018

and

was included in other long-term liabilities.

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

Defined Benefit Pension Plans

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 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 Taiwan, Korea and Japan.

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.

The net periodic benefit costs for the plans included the following components:


	Year Ended December 31,
	2019			2018
Service cost	$	828		$	657
Interest cost on projected benefit obligations		471			433
Expected return on plan assets		(111	)		(115	)
Amortization of actuarial net loss		136			127

	$	1,324		$	1,102

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,
	2019			2018
Change in projected benefit obligations:
Projected benefit obligations, beginning of year	$	24,885		$	25,736
Assumed in ESI Merger		3,522			—
Service cost		828			657
Interest cost		471			433
Actuarial loss (gain)		2,057			(98	)
Benefits paid		(1,469	)		(895	)
Currency translation adjustments		(242	)		(948	)

Projected benefit obligations, end of year	$	30,052		$	24,885

Change in plan assets:
Fair value of plan assets, beginning of year	$	7,822		$	8,152
Assumed in ESI Merger		1,272			—
Company contributions		1,846			324
Gain (loss) on plan assets		591			(56	)
Benefits paid		(569	)		(369	)
Currency translation adjustments		131			(229	)

Fair value of plan assets, end of year		11,093			7,822

Net underfunded status	$	(18,959	)	$	(17,063	)

As of December

2019

, the estimated benefit payments for the Company’s defined benefit plans for the next

years were as follows:


	Estimated benefit payments
2020	$	1,133
2021		1,302
2022		1,217
2023		1,537
2024		1,483
2025-2029		8,646

	$	15,318

The Company expects to contribute $2,086 to the plans

during 2020.

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


	December 31, 2019			December 31, 2018
Discount rate		1.4	%		1.9	%
Rate of increase in salary levels		2.2	%		2.1	%
Expected long-term rate of return on assets		2.1	%		1.9	%

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:


	Year Ended December 31, 2019					Year Ended December 31, 2018
	Amount		Percentage			Amount		Percentage
Cash	$	430		4	%	$	193		2	%
Debt securities		8,023		72			4,855		62
Equity securities		1,519		14			1,342		17
Other		1,121		10			1,432		19

	$	11,093		100	%	$	7,822		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 $16,713 and vested benefit obligations of $19,692 as of December 31, 2019 and assets of $14,409 and vested benefit obligations of $17,552 as of December 31, 2018. Under the shut-down method, the liability is calculated as if it were payable as of the balance sheet date, on an undiscounted basis.

Other Pension-Related Assets

As of December 31, 2019 and 2018, the Company had assets with an aggregate market value of $5,854 and $5,890, 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. The Germany contracts have a guaranteed minimum rate of return ranging from 2.25% to 4.25%, depending on the contract. Because the 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.