Pension and other postretirement benefits (Tables)

6 Months Ended

Jun. 26, 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 Six Months Ended						Other Postretirement Benefits Six Months Ended
	June 26, 2016			June 28, 2015			June 26, 2016		June 28, 2015		June 26, 2016			June 28, 2015			June 26, 2016		June 28, 2015
	(Dollars in thousands)
Service cost	$	655		$	469		$	111	$	107	$	1,307		$	940		$	222	$	214
Interest cost	3,929			4,485			407		511		7,849			8,971			813		1,023
Expected return on plan assets	(6,199		)	(6,427		)	—		—		(12,397		)	(12,852		)	—		—
Net amortization and deferral	1,577			1,528			57		78		3,156			3,058			114		155
Net benefits expense (income)	$	(38	)	$	55		$	575	$	696	$	(85	)	$	117		$	1,149	$	1,392