Pension and other postretirement benefits (Tables)

9 Months Ended

Oct. 01, 2017

Compensation and Retirement Disclosure [Abstract]

Net Benefit Cost of Pension and Postretirement Benefit Plans

Net pension and other postretirement benefits expense (income) consist of the following:

	Pension Three Months Ended						Other Postretirement Benefits Three Months Ended				Pension Nine Months Ended						Other Postretirement Benefits Nine Months Ended
	October 1, 2017			September 25, 2016			October 1, 2017		September 25, 2016		October 1, 2017			September 25, 2016			October 1, 2017		September 25, 2016
	(Dollars in thousands)
Service cost	$	725		$	656		$	61	$	44	$	2,162		$	1,963		$	210	$	266
Interest cost	3,773			3,948			426		383		11,347			11,797			1,183		1,196
Expected return on plan assets	(6,607		)	(6,209		)	—		—		(20,100		)	(18,606		)	—		—
Net amortization and deferral	1,668			1,781			75		63		5,049			4,937			206		177
Net benefits expense (income)	$	(441	)	$	176		$	562	$	490	$	(1,542	)	$	91		$	1,599	$	1,639