Pension plans and other postretirement benefits (Tables)

9 Months Ended

Sep. 30, 2016

Compensation And Retirement Disclosure [Abstract]

Net Periodic Defined Benefit Cost for Defined Benefit Plans

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

	Pension benefits						Other postretirement benefits
	Three months ended September 30
	2016			2015			2016			2015
	(in thousands)
Service cost	$	6,259			5,916			399		188
Interest cost on projected benefit obligation		20,853			17,754			1,242		651
Expected return on plan assets		(27,118	)		(23,527	)		—			—
Amortization of prior service credit		(807	)		(1,501	)		(339	)		(340	)
Amortization of net actuarial loss		7,536			11,207			15		26
Net periodic benefit cost	$	6,723			9,849			1,317		525

	Pension benefits						Other postretirement benefits
	Nine months ended September 30
	2016			2015			2016			2015
	(in thousands)
Service cost	$	18,778			17,748			1,197			562
Interest cost on projected benefit obligation		62,558			53,261			3,728			1,953
Expected return on plan assets		(81,355	)		(70,578	)		—			—
Amortization of prior service credit		(2,421	)		(4,504	)		(1,019	)		(1,019	)
Amortization of net actuarial loss		22,609			33,619			45			79
Net periodic benefit cost	$	20,169			29,546			3,951			1,575