Pension and Other Postretirement Benefits - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended	6 Months Ended		12 Months Ended
	Oct. 31, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2017	Aug. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Reduction in long-term pension liabilities		$ 18,700,000
General Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discretionary contribution	$ 100,000,000
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment charge		$ 500,000	$ 500,000	$ 0
Discount rate						3.57%
Pension Plans | Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions					$ 0