Benefit Plans - Other Post-Retirement Benefits (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015 USD ($) age	Dec. 31, 2014 USD ($)
Schedule of Defined Benefit Plans and Defined Contribution Plans Disclosures [Line Items]
Post-retirement medical, maximum age of coverage | age		65
Post-retirement medical, minimum service requirement		5 years
Post-retirement medical, minimum age of coverage | age		55
Post-retirement medical, post 55, pre 2006 employee percentage of monthly insurance		20.00%
Post-retirement medical, post 55, post 2006 employee percentage of monthly insurance		100.00%
Post-retirement medical, post 2006 reduction in premium service requirement		10 years
Post-retirement medical, post 55 with post 2006 reduction in premium service requirement percentage of monthly insurance		50.00%
Weighted-average discount rates used to determine the benefit obligations	4.20%		3.50%
Weighted average discount rate use to determine net periodic benefit costs	3.80%	3.50%	4.50%
Postretirement Medical Plan
Schedule of Defined Benefit Plans and Defined Contribution Plans Disclosures [Line Items]
Plan termination | $		$ 6,632	$ 0
Defined benefit gain on plan termination | $		$ (5,600)