Employee Benefit Plans Employee Benefit Plans - Additional Information (Details)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) hour	Sep. 30, 2017 USD ($) hour	Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of hours | hour	1,000	1,000
Curtailment gain		$ 17,244,000
Unrecognized prior service cost	$ 1,852,000
Actuarial loss	$ 15,392,000
Net curtailment gain including recognition of prior service cost and actuarial loss		$ 0
Scenario, Forecast | Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			$ 0
Scenario, Forecast | Post-Retirement Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			708,000
Scenario, Forecast | Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			$ 3,336,000