Pension plans and other postretirement benefits (Tables)

6 Months Ended

Jun. 30, 2011

Pension plans and other postretirement benefits (Tables) [Abstract]

Net periodic benefit cost for defined benefit plans

							Other
	Pension						postretirement
	benefits						benefits
	Three months ended June 30
	2011			2010			2011		2010
				(in thousands)
Service cost	$	6,413			4,960			115		102
Interest cost on projected benefit obligation		14,086			12,032			909		785
Expected return on plan assets		(14,563	)		(12,655	)		—		—
Amortization of prior service cost		(1,629	)		(1,629	)		29		63
Amortization of net actuarial loss		5,165			3,455			18		(5	)
Net periodic benefit cost	$	9,472			6,163			1,071		945

							Other
	Pension						postretirement
	benefits						benefits
				Six months ended June 30
	2011			2010			2011		2010
				(in thousands)
Service cost	$	11,713			9,835			240		202
Interest cost on projected benefit obligation		26,236			24,061			1,684		1,565
Expected return on plan assets		(27,263	)		(25,443	)		—		—
Amortization of prior service cost		(3,279	)		(3,279	)		54		88
Amortization of net actuarial loss		10,265			6,776			18		(5	)
Net periodic benefit cost	$	17,672			11,950			1,996		1,850