Pension Plan and Other Postretirement Benefits (Tables)

6 Months Ended

Jun. 30, 2016

Compensation and Retirement Disclosure [Abstract]

Schedule of components of net periodic benefit costs for the pension plans and other postretirement benefits

The following table lists components of net periodic benefit costs for the pension plans and other postretirement benefits. The data listed under “pension plan” includes the qualified pension plan and the non-qualified supplemental executive retirement plan. The data listed under “other benefits” is for all other postretirement benefits.

	Three Months Ended June 30
	Pension Plan						Other Benefits
	2016			2015			2016			2015
Service cost	$	5,067		$	5,632		$	2,304		$	2,500
Interest cost	5,453			5,003			1,800			1,614
Expected return on plan assets	(5,454		)	(4,792		)	(1,046		)	(876		)
Amortization of prior service cost	1,555			1,502			11			11
Recognized net actuarial loss	1,293			2,400			1,261			1,458
Net periodic benefit cost	$	7,914		$	9,745		$	4,330		$	4,707

	Six Months Ended June 30
	Pension Plan						Other Benefits
	2016			2015			2016			2015
Service cost	$	10,134		$	11,265		$	4,608		$	5,001
Interest cost	10,906			10,006			3,600			3,227
Expected return on plan assets	(10,908		)	(9,584		)	(2,092		)	(1,752		)
Amortization of prior service cost	3,109			3,004			22			22
Recognized net actuarial loss	2,586			4,800			2,523			2,917
Net periodic benefit cost	$	15,827		$	19,491		$	8,661		$	9,415