Pension and Other Postretirement Benefits (Tables)

6 Months Ended

Jun. 30, 2017

Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]

Schedule of Net Benefit Costs

The net periodic benefit cost for the three and six months ended June 30, 2017 and 2016 includes the following components: 

	Pension Benefits						Postretirement Benefits
	Three Months Ended   June 30,						Three Months Ended   June 30,
Components of Net Periodic Benefit Cost	2017			2016			2017			2016
Service cost	$	6,508		$	6,309		$	588		$	569
Interest cost	6,909			7,006			722			740
Expected return on plan assets	(7,590		)	(6,733		)	—			—
Amortization of:
Net actuarial loss	5,451			4,632			169			154
Prior service cost (gain)	110			112			(540		)	(540		)
Net periodic benefit cost	$	11,388		$	11,326		$	939		$	923
	Pension Benefits						Postretirement Benefits
	Six Months Ended   June 30,						Six Months Ended   June 30,
Components of Net Periodic Benefit Cost	2017			2016			2017			2016
Service cost	$	13,208		$	12,684		$	1,163		$	1,144
Interest cost	13,909			14,131			1,422			1,515
Expected return on plan assets	(15,315		)	(13,508		)	—			—
Amortization of:
Net actuarial loss	10,751			9,582			394			354
Prior service cost (gain)	210			212			(1,090		)	(1,090		)
Net periodic benefit cost	$	22,763		$	23,101		$	1,889		$	1,923