Pension plans and other postretirement benefits (Tables)

3 Months Ended

Mar. 31, 2018

Compensation And Retirement Disclosure [Abstract]

Net Periodic Defined Benefit Cost for Defined Benefit Plans

Net periodic defined benefit cost for defined benefit plans consisted of the following:

	Pension Benefits						Other Postretirement Benefits
	Three Months Ended March 31
	2018			2017			2018			2017
	(In thousands)
Service cost	$	5,103			4,908			226		383
Interest cost on projected benefit obligation		18,805			19,691			557			1,080
Expected return on plan assets		(30,875	)		(27,200	)		—			—
Amortization of prior service cost (credit)		125			125			(1,175	)		(350	)
Amortization of net actuarial loss		11,100			6,800			(200	)		(25	)
Net periodic benefit cost	$	4,258			4,324			(592	)		1,088