Pension plans and other postretirement benefits (Tables)

3 Months Ended

Mar. 31, 2013

Compensation And Retirement Disclosure [Abstract]

Net Periodic Benefit Cost 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
	2013			2012			2013			2012
	(in thousands)
Service cost	$	6,050			7,900			200			175
Interest cost on projected benefit obligation		15,126			15,600			675			950
Expected return on plan assets		(21,875	)		(17,675	)		—			—
Amortization of prior service credit		(1,650	)		(1,650	)		(350	)		—
Amortization of net actuarial loss		10,400			9,400			100			100
Net periodic benefit cost	$	8,051			13,575			625			1,225