Employee Benefits Plans (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) Age	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 Age
Defined Benefit Plan Disclosure [Line Items]
Pension benefits		$ 455,736	$ 488,682
one-time non-cash charge		8,000
Pension plans, accumulated other comprehensive income (loss)		13,000
Pension settlement		(7,650)	509	$ (12,564)
Payments for postemployment benefits			$ 224,000
Settlement percentage of pension obligation			12.00%
Pension lump sum settlement expense		$ 0	$ 0	97,231
U.S. pension plan assets percentage of total pension plan assets		74.00%
Required pension contributions to our pension plans		$ 22,000
Deferred compensation		49,533	43,943
Non-qualified supplemental pension plan
Defined Benefit Plan Disclosure [Line Items]
Pension benefits		53,000	51,000
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Pension settlement				(259,000)
Net actuarial loss to be recognized		34,000
Deferred compensation		$ 50,000	44,000
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Maximum age limit of qualified retirees for health care benefits | Age		65
Modified age limit of qualified retirees for health care benefits | Age					52
Modified years of service required for qualified retirees for health care benefits					12 years
Assumed change in healthcare cost trend rates in each year		1.00%
Defined Contribution Savings Plan
Defined Benefit Plan Disclosure [Line Items]
Expense related to defined contribution savings plans		$ 38,000	38,000	$ 35,000
Rabbi Trusts
Defined Benefit Plan Disclosure [Line Items]
Assets held in trust		50,000	43,000
Value of common stock issued in trust		$ 2,000	$ 1,000
Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Pension and other postretirement benefit expense	$ 2,000