Pension Plan and Other Postretirement Benefits (Tables)

9 Months Ended

Sep. 30, 2015

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 September 30
	Pension Plan						Other Benefits
	2015			2014			2015			2014
Service cost	$	4,715		$	3,539		$	3,043		$	1,398
Interest cost	5,072			4,737			2,101			1,321
Expected return on plan assets	(4,770		)	(4,091		)	(908		)	(832		)
Amortization of prior service cost	1,502			1,527			12			11
Recognized net actuarial loss	2,308			1,002			2,182			656
Net periodic benefit cost	$	8,827		$	6,714		$	6,430		$	2,554

	Nine Months Ended September 30
	Pension Plan						Other Benefits
	2015			2014			2015			2014
Service cost	$	15,980		$	11,973		$	8,044		$	4,637
Interest cost	15,078			14,190			5,328			3,995
Expected return on plan assets	(14,354		)	(12,449		)	(2,660		)	(2,339		)
Amortization of prior service cost	4,506			4,547			34			33
Recognized net actuarial loss	7,108			3,008			5,099			2,206
Net periodic benefit cost	$	28,318		$	21,269		$	15,845		$	8,532