Employee benefit plans (Tables)

3 Months Ended

Mar. 31, 2018

Retirement Benefits [Abstract]

Schedule of net benefit costs

Components of net periodic benefit cost (credit) for the Company's pension and other postretirement benefit plans were as follows:

	Pension Benefits						Other Postretirement Benefits
Three Months Ended March 31,	2018			2017			2018			2017
	(In thousands)
Components of net periodic benefit cost (credit):
Service cost	$	—		$	—		$	407		$	447
Interest cost	3,807			4,014			778			808
Expected return on assets	(4,998		)	(5,029		)	(1,167		)	(1,145		)
Amortization of prior service credit	—			—			(349		)	(343		)
Amortization of net actuarial loss	1,782			1,793			238			336
Net periodic benefit cost (credit), including amount capitalized	591			778			(93		)	103
Less amount capitalized	—			107			40			(39		)
Net periodic benefit cost (credit)	$	591		$	671		$	(133	)	$	142