Pension and Savings Plans (Details Textuals)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016 USD ($) years plans	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Estimated prior service cost that will be amortized from accumulated other comprehensive loss		$ 4,500,000	$ (10,400,000)	$ (11,400,000)
Settlement Charge		$ 21,700,000	29,600,000	28,300,000
Defined Contribution Plans [Abstract]
Number of 401(k) plans | plans		2
Paid discretionary contributions to defined contribution pension plans, company match		$ 19,200,000	22,000,000	44,700,000
Additional discretionary contributions to defined contribution pension plans, performance feature			$ 19,500,000	18,300,000
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Settlements, Benefit Obligation				$ 41,700,000
Actuarial gains and losses amortization corridor, percentage		5.00%
Period of amortization (in years) | years		5
Estimated net actuarial loss that will be amortized from accumulated other comprehensive loss		$ 25,400,000
Estimated prior service cost that will be amortized from accumulated other comprehensive loss		$ 300,000
Expected rate of return on plan assets	5.90%	6.00%	6.25%	6.85%
Accumulated benefit obligation for pension plans		$ 959,300,000	$ 939,300,000
Minimum funded percentage defined by the Pension Protection Act of 2006		80.00%
Pension and Other Postretirement Benefit Contributions		$ 500,000
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year		5,900,000
Settlement Charge		0	$ 0	$ 8,700,000
Other Pension Plan, Postretirement or Supplemental Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefit Contributions		$ 600,000
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for assets of Master Trust			31.00%
Fixed Income Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for assets of Master Trust			69.00%
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for assets of Master Trust		2.00%	3.00%