Employee Benefit Plans

3 Months Ended

Mar. 31, 2016

Compensation and Retirement Disclosure [Abstract]

Employee Benefit Plans

Employee Benefit Plans

We sponsor two pension plans for certain union employees and a pension plan primarily for non-union employees, a postretirement benefit plan for selected employees and a defined contribution plan. The following tables present our consolidated net periodic benefit costs related to the pension and postretirement benefit plans for the three months ended March 31, 2015 and 2016 (in thousands):

	Three Months Ended						Three Months Ended
	March 31, 2015						March 31, 2016
	Pension Benefits			Other  Postretirement Benefits			Pension Benefits			Other  Postretirement Benefits
Components of net periodic benefit costs:
Service cost	$	4,470		$	66		$	4,688		$	61
Interest cost	1,869			110			2,045			110
Expected return on plan assets	(1,896		)	—			(2,128		)	—
Amortization of prior service credit	—			(928		)	(45		)	(928		)
Amortization of actuarial loss	1,347			225			1,217			184
Net periodic benefit cost (credit)	$	5,790		$	(527	)	$	5,777		$	(573	)

Contributions estimated to be paid into the plans in 2016 are $22.9 million and $0.5 million for the pension and other postretirement benefit plans, respectively.

We match our employees’ qualifying contributions to our defined contribution plan, resulting in expense to us. Expenses related to the defined contribution plan were $2.8 million and $3.0 million, respectively, for the three months ended March 31, 2015 and 2016.

Amounts Included in AOCL

The changes in AOCL related to employee benefit plan assets and benefit obligations for the three months ended March 31, 2015 and 2016 were as follows (in thousands):

	Three Months Ended						Three Months Ended
	March 31, 2015						March 31, 2016
Gains (Losses) Included in AOCL	Pension Benefits			Other Postretirement Benefits			Pension Benefits			Other Postretirement Benefits
Beginning balance	$	(63,257	)	$	(1,696	)	$	(62,279	)	$	(3,945	)
Amortization of prior service credit	—			(928		)	(45		)	(928		)
Amortization of actuarial loss	1,347			225			1,217			184
Ending balance	$	(61,910	)	$	(2,399	)	$	(61,107	)	$	(4,689	)