8. Employee Benefit Plans and Other Postretirement Plans

For the three- and nine-month periods ended September 30, 2013 and 2012, net pension costs were comprised of the following:


	Three Months Ended September 30,						Nine Months Ended September 30,
	2013			2012			2013			2012
(In thousands)
Components of Net Pension Costs
Service cost for benefits earned during the year	$	5,825		$	5,606		$	18,322		$	16,818
Interest cost on accumulated benefit obligation		4,269			3,700			12,250			11,100
Expected return on assets		(3,796	)		(3,027	)		(11,297	)		(9,081	)
Net amortization of unrecognized amounts
Prior service cost		163			1,498			3,284			4,495
Curtailment loss		3,132			—			10,908			—
Actuarial loss		2,217			1,229			5,220			3,687

Net pension costs	$	11,810		$	9,006		$	38,687		$	27,019

In June 2013, the United Steelworkers (“USW”) ratified a master labor agreement with PCA under which certain USW-represented corrugated plant employees will have pension accruals frozen under PCA’s hourly pension plan. As of the date of the pension freeze, affected USW-represented employees will transition to a defined contribution 401k plan for future service. In accordance with ASC 715, “Compensation — Retirement Benefits,” the Company recorded a $7.8 million pre-tax pension curtailment charge related to the unrecognized prior service costs of employees impacted by the pension freeze during the second quarter of 2013. The Company also remeasured the hourly pension plan benefit obligation using current fair values of plan assets and current assumptions, resulting in a decrease in the benefit obligation of $13.8 million with a corresponding decrease in accumulated other comprehensive income (loss) of $8.4 million and deferred taxes of $5.4 million.

In September 2013, the USW ratified a master labor agreement with PCA under which certain USW-represented containerboard mill employees will have pension accruals frozen under PCA’s hourly pension plan. As of the date of the pension freeze, affected USW-represented employees will transition to a defined contribution 401k plan for future service. The Company recorded a $3.1 million pre-tax pension curtailment charge related to the unrecognized prior service costs of employees impacted by the pension freeze during the third quarter of 2013. The Company also remeasured the hourly pension plan benefit obligation using current fair values of plan assets and current assumptions, resulting in a decrease in the benefit obligation of $8.1 million with a corresponding decrease in accumulated other comprehensive income (loss) of $5.0 million and deferred taxes of $3.1 million.

The Company makes pension plan contributions that are sufficient to fund its actuarially determined costs, generally equal to the minimum amounts required by the Employee Retirement Income Security Act (ERISA). However, from time to time the Company may make discretionary contributions in excess of the required minimum amounts. The Company contributed $30.0 million to the pension plans in September 2013.

For the three- and nine-month periods ended September 30, 2013 and 2012, net postretirement costs relating to certain medical benefits for retirees were comprised of the following:


	Three Months Ended September 30,						Nine Months Ended September 30,
	2013			2012			2013			2012
(In thousands)
Components of Net Postretirement Costs
Service cost for benefits earned during the year	$	515		$	464		$	1,545		$	1,392
Interest cost on accumulated benefit obligation		311			310			934			931
Net amortization of unrecognized amounts
Prior service cost		(106	)		(104	)		(319	)		(314	)
Actuarial loss		134			113			401			339

Net postretirement costs	$	854		$	783		$	2,561		$	2,348