Pension and other postretirement benefits (Tables)

9 Months Ended

Sep. 25, 2016

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
	September 25, 2016			September 27, 2015			September 25, 2016		September 27, 2015		September 25, 2016			September 27, 2015			September 25, 2016		September 27, 2015
	(Dollars in thousands)
Service cost	$	656		$	470		$	44	$	157	$	1,963		$	1,410		$	266	$	371
Interest cost	3,948			4,492			383		452		11,797			13,463			1,196		1,476
Expected return on plan assets	(6,209		)	(6,606		)	—		—		(18,606		)	(19,457		)	—		—
Net amortization and deferral	1,781			1,563			63		8		4,937			4,620			177		162
Net benefits expense (income)	$	176		$	(81	)	$	490	$	617	$	91		$	36		$	1,639	$	2,009