Employee benefit plans (Tables)

3 Months Ended

Mar. 31, 2017

Compensation and Retirement Disclosure [Abstract]

Schedule of net benefit costs

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

	Pension Benefits						Other Postretirement Benefits
Three Months Ended March 31,	2017			2016			2017			2016
	(In thousands)
Components of net periodic benefit cost:
Service cost	$	—		$	—		$	447		$	450
Interest cost	4,014			4,390			808			949
Expected return on assets	(5,029		)	(5,280		)	(1,145		)	(1,149		)
Amortization of prior service credit	—			—			(343		)	(343		)
Amortization of net actuarial loss	1,793			1,593			336			448
Net periodic benefit cost, including amount capitalized	778			703			103			355
Less amount capitalized	107			81			(39		)	34
Net periodic benefit cost	$	671		$	622		$	142		$	321