Employee benefit plans (Tables)

9 Months Ended

Sep. 30, 2017

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 September 30,	2017			2016			2017			2016
	(In thousands)
Components of net periodic benefit cost (credit):
Service cost	$	—		$	—		$	377		$	412
Interest cost	4,052			4,305			816			922
Expected return on assets	(5,132		)	(5,231		)	(1,160		)	(1,133		)
Amortization of prior service credit	—			—			(343		)	(343		)
Amortization of net actuarial loss	1,589			1,553			213			371
Net periodic benefit cost (credit), including amount capitalized	509			627			(97		)	229
Less amount capitalized	65			82			(95		)	(34		)
Net periodic benefit cost (credit)	$	444		$	545		$	(2	)	$	263

	Pension Benefits						Other Postretirement Benefits
Nine Months Ended September 30,	2017			2016			2017			2016
	(In thousands)
Components of net periodic benefit cost (credit):
Service cost	$	—		$	—		$	1,130		$	1,236
Interest cost	12,155			12,915			2,449			2,766
Expected return on assets	(15,395		)	(15,693		)	(3,480		)	(3,400		)
Amortization of prior service credit	—			—			(1,029		)	(1,029		)
Amortization of net actuarial loss	4,767			4,660			649			1,118
Net periodic benefit cost (credit), including amount capitalized	1,527			1,882			(281		)	691
Less amount capitalized	245			284			(248		)	4
Net periodic benefit cost (credit)	$	1,282		$	1,598		$	(33	)	$	687