Pension and Other Postretirement Benefits (Tables)

6 Months Ended

Jun. 30, 2015

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, 2015 and 2014 included the following components: 

	Pension Benefits						Postretirement Benefits
	Three Months Ended   June 30,						Three Months Ended   June 30,
Components of Net Periodic Benefit Cost	2015			2014			2015			2014
Service cost	$	6,304		$	5,506		$	577		$	602
Interest cost	6,251			6,610			713			843
Expected return on plan assets	(7,123		)	(6,637		)	—			—
Amortization of:
Net actuarial loss	5,090			4,285			271			359
Prior service cost (gain)	113			230			(545		)	(540		)
Net periodic benefit cost	$	10,635		$	9,994		$	1,016		$	1,264

	Pension Benefits						Postretirement Benefits
	Six Months Ended   June 30,						Six Months Ended   June 30,
Components of Net Periodic Benefit Cost	2015			2014			2015			2014
Service cost	$	12,804		$	11,103		$	1,252		$	1,227
Interest cost	12,601			13,409			1,463			1,668
Expected return on plan assets	(14,148		)	(13,312		)	—			—
Amortization of:
Net actuarial loss	10,014			8,819			522			634
Prior service cost (gain)	226			476			(1,090		)	(1,090		)
Settlement loss	—			789			—			—
Net periodic benefit cost	$	21,497		$	21,284		$	2,147		$	2,439