Pension plans and other postretirement benefits (Tables)

6 Months Ended

Jun. 30, 2012

Pension plans and other postretirement benefits [Abstract]

Net periodic benefit cost for defined benefit plans

	Pension benefits						Other postretirement benefits
	Three months ended June 30
	2012			2011			2012		2011
	(in thousands)
Service cost	$	6,875			6,413			159		115
Interest cost on projected benefit obligation		15,418			14,086			919		909
Expected return on plan assets		(17,581	)		(14,563	)		—		—
Amortization of prior service cost		(1,629	)		(1,629	)		10		29
Amortization of net actuarial loss		9,183			5,165			165		18
Net periodic benefit cost	$	12,266			9,472			1,253		1,071

	Pension benefits						Other postretirement benefits
	Six months ended June 30
	2012			2011			2012		2011
	(in thousands)
Service cost	$	14 ,775			11,713			334		240
Interest cost on projected benefit obligation		31,018			26,236			1,869		1,684
Expected return on plan assets		(35,256	)		(27,263	)		—		—
Amortization of prior service cost		(3,279	)		(3,279	)		10		54
Amortization of net actuarial loss		18,583			10,265			265		18
Net periodic benefit cost	$	25,841			17,672			2,478		1,996