Employee benefit plans (Tables)

6 Months Ended

Jun. 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 June 30,	2017			2016			2017			2016
	(In thousands)
Components of net periodic benefit cost (credit):
Service cost	$	—		$	—		$	306		$	374
Interest cost	4,089			4,220			825			895
Expected return on assets	(5,234		)	(5,182		)	(1,175		)	(1,118		)
Amortization of prior service credit	—			—			(343		)	(343		)
Amortization of net actuarial loss	1,385			1,514			100			299
Net periodic benefit cost (credit), including amount capitalized	240			552			(287		)	107
Less amount capitalized	73			121			(114		)	4
Net periodic benefit cost (credit)	$	167		$	431		$	(173	)	$	103

	Pension Benefits						Other Postretirement Benefits
Six Months Ended June 30,	2017			2016			2017			2016
	(In thousands)
Components of net periodic benefit cost (credit):
Service cost	$	—		$	—		$	753		$	824
Interest cost	8,103			8,610			1,633			1,844
Expected return on assets	(10,263		)	(10,462		)	(2,320		)	(2,267		)
Amortization of prior service credit	—			—			(686		)	(686		)
Amortization of net actuarial loss	3,178			3,107			436			747
Net periodic benefit cost (credit), including amount capitalized	1,018			1,255			(184		)	462
Less amount capitalized	180			202			(153		)	38
Net periodic benefit cost (credit)	$	838		$	1,053		$	(31	)	$	424