Defined Contribution Plans—Eligible employees currently participate in a defined contribution profit sharing and savings plan ("PSSP") that we sponsor. The PSSP covers all regular full-time employees. PSSP participants may elect to make voluntary contributions to this plan up to a specified amount of their compensation. We make matching contributions based on a percent of an employee's eligible compensation and also make an additional non-matching contribution. Our contribution expense for the PSSP was approximately $21.1 million, $19.9 million and $18.7 million for the years ended December 31, 2019, 2018 and 2017, respectively.

Defined Benefit Plan—Eligible employees and former employees of certain of our mining operations participate in a defined benefit plan (the "Pension Plan") that we sponsor. The Pension Plan is closed to new applicants. Participants in the Pension Plan are no longer receiving benefit accruals for service. Participants can participate in enhanced benefits provisions under the PSSP. The benefit formula for the Pension Plan is a fixed-dollar unit based on years of service.

The following sets forth changes in benefit obligations and plan assets for the years ended December 31, 2019 and 2018 and the funded status of the Pension Plan reconciled with the amounts reported in our consolidated financial statements:

The actuarial loss component of the change in benefit obligation in 2019 was primarily attributable to a decrease in the discount rate compared to December 31, 2018, offset in part by updated mortality tables. The actuarial gain component of the change in benefit obligation in 2018 was primarily attributable to an increase in the discount rate compared to December 31, 2017 and updated mortality tables, offset in part by decreases in expected retirements and other demographic changes.

The expected long-term rate of return used to determine our pension liability is based on a 1.5% active management premium in addition to an asset allocation assumption of:

The actual return on plan assets was 19.2% and a loss of 6.7% for the years ended December 31, 2019 and 2018, respectively.

(1)	Nonservice components of net periodic benefit cost are included in the Other income (expense) line item within our consolidated statements of income (see Note 2 – Summary of Significant Accounting Policies).


	Year Ended December 31,
	2019		2018
	(in thousands)
Other changes in plan assets and benefit obligation recognized in accumulated other comprehensive loss:
Net actuarial loss	$	(7,350)	$	(3,326)
Reversal of amortization item:
Prior service cost		186		186
Net actuarial loss		3,922		3,608
Total recognized in accumulated other comprehensive loss		(3,242)		468
Net periodic benefit cost		(4,040)		(2,472)
Total recognized in net periodic benefit cost and accumulated other comprehensive loss	$	(7,282)	$	(2,004)

Estimated future benefit payments as of December 31, 2019 are as follows:


Year Ended
December 31,	(in thousands)

2020	$	5,288
2021		5,677
2022		6,045
2023		6,342
2024		6,507
2025-2029		34,755
	$	64,614

We expect to contribute $5.3 million to the Pension Plan in 2020.

The Compensation Committee has appointed an investment manager with full investment authority with respect to Pension Plan investments subject to investment guidelines and compliance with ERISA or other applicable laws. The investment manager employs a series of asset allocation strategy phases to glide the portfolio risk commensurate with both plan characteristics and market conditions. The objective of the allocation policy is to reach and maintain fully funded status. The total portfolio allocation will be adjusted as the funded ratio of the Pension Plan changes and market conditions warrant. The target allocation includes investments in equity and fixed income commingled investment funds. Total account performance is reviewed at least annually, using a dynamic benchmark approach to track investment performance. General asset allocation guidelines at December 31, 2019 are as follows:


	Percentage of Total Portfolio
	Minimum	Target	Maximum

Equity securities	45%	62%	80%
Fixed income securities	10%	33%	55%
Real estate	0%	5%	10%

Equity securities include domestic equity securities, developed international securities, emerging markets equity securities and real estate investment trust. Fixed income securities include domestic and international investment grade fixed income securities, high yield securities and emerging markets fixed income securities. Fixed income futures may also be utilized within the fixed income securities asset allocation.

The following information discloses the fair values of our Pension Plan assets by asset category:


	December 31,
	2019		2018
	(in thousands)
Cash and cash equivalents (a)	$	2,958	$	5,277

Commingled investment funds measured at net asset value (b):
Equities - Global		10,028		—
Equities - United States large-cap		19,220		21,862
Equities - United States small-cap		7,592		5,259
Equities - International developed markets		10,528		10,593
Equities - International emerging markets		8,410		4,808
Fixed income - Investment grade		26,186		15,777
Fixed income - High yield		—		4,508
Real estate		4,355		5,034
Other		2,290		2,705
Total	$	91,567	$	75,823

(a)	Cash and cash equivalents represents a Level 1 fair value measurement. See Note 2 – Summary of Significant Accounting Policies – Fair Value Measurements for more information regarding the definitions of fair value hierarchy levels.

(b)

Investments measured at fair value using the net asset value per share (or its equivalent) have not been classified within the fair value hierarchy. The fair values of all commingled investment funds are determined based on the net asset values per unit of each of the funds. The net asset values per unit represent the aggregate value of the fund's assets at fair value less liabilities, divided by the number of units outstanding.

See Note 2 – Summary of Significant Accounting Policies for more information on our accounting policy for pension benefits.