Employee benefit plans (Tables)

6 Months Ended

Jun. 30, 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 June 30,	2018			2017			2018			2017
	(In thousands)
Components of net periodic benefit cost (credit):
Service cost	$	—		$	—		$	340		$	306
Interest cost	3,488			4,089			672			825
Expected return on assets	(5,379		)	(5,234		)	(1,266		)	(1,175		)
Amortization of prior service credit	—			—			(348		)	(343		)
Amortization of net actuarial loss	1,721			1,385			82			100
Net periodic benefit cost (credit), including amount capitalized	(170		)	240			(520		)	(287		)
Less amount capitalized	—			73			43			(114		)
Net periodic benefit cost (credit)	$	(170	)	$	167		$	(563	)	$	(173	)

	Pension Benefits						Other Postretirement Benefits
Six Months Ended June 30,	2018			2017			2018			2017
	(In thousands)
Components of net periodic benefit cost (credit):
Service cost	$	—		$	—		$	747		$	753
Interest cost	7,295			8,103			1,450			1,633
Expected return on assets	(10,377		)	(10,263		)	(2,433		)	(2,320		)
Amortization of prior service credit	—			—			(697		)	(686		)
Amortization of net actuarial loss	3,503			3,178			320			436
Net periodic benefit cost (credit), including amount capitalized	421			1,018			(613		)	(184		)
Less amount capitalized	—			180			83			(153		)
Net periodic benefit cost (credit)	$	421		$	838		$	(696	)	$	(31	)