Pension plans and other postretirement benefits (Tables)

3 Months Ended

Mar. 31, 2014

Compensation And Retirement Disclosure [Abstract]

Net Periodic Pension Expense for Defined Benefit Plans

Net periodic benefit cost for defined benefit plans consisted of the following:

	Pension benefits						Other postretirement benefits
	Three months ended March 31
	2014			2013			2014			2013
	(in thousands)
Service cost	$	5,100			6,050			150			200
Interest cost on projected benefit obligation		17,250			15,126			675			675
Expected return on plan assets		(22,925	)		(21,875	)		—			—
Amortization of prior service credit		(1,650	)		(1,650	)		(350	)		(350	)
Amortization of net actuarial loss		3,350			10,400			—			100
Net periodic benefit cost	$	1,125			8,051			475			625