Pension and other postretirement benefits (Tables)

6 Months Ended

Jun. 28, 2015

Compensation and Retirement Disclosure [Abstract]

Net Benefit Cost of Pension and Postretirement Benefit Plans

Net benefit cost of pension and postretirement benefit plans consisted of the following:

	Pension Three Months Ended						Other Postretirement Benefits Three Months Ended				Pension Six Months Ended						Other Postretirement Benefits Six Months Ended
	June 28, 2015			June 29, 2014			June 28, 2015		June 29, 2014		June 28, 2015			June 29, 2014			June 28, 2015		June 29, 2014
	(Dollars in thousands)
Service cost	$	469		$	447		$	107	$	138	$	940		$	897		$	214	$	276
Interest cost	4,485			4,486			$	511	596		8,971			8,969			1,023		1,193
Expected return on plan assets	(6,427		)	(6,264		)	$	—	—		(12,852		)	(12,524		)	—		—
Net amortization and deferral	1,528			1,070			$	78	27		3,058			2,141			155		53
Net benefit expense (income)	$	55		$	(261	)	$	696	$	761	$	117		$	(517	)	$	1,392	$	1,522