Employee Benefit Plans and Other Postretirement Benefits (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Retirement age threshold		55 years
Postretirement benefits eligibility, years of service requirement		10 years
Period over which asset gain (losses) are amortized		5 years
Company contributions		$ 19,000	$ 18,200	$ 18,000
Pension and SERPA Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		2,100,000	1,900,000
Projected benefit obligations		$ 2,201,021	$ 1,986,435	$ 2,009,000
Expected return on plan assets		7.25%	7.50%	7.75%
Company contributions		$ 25,000	$ 25,000
Pension Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Investment in company common stock - shares		1,273,592	1,273,592
Investment in company common stock - value		$ 64,800	$ 74,300
Company contributions		$ 25,000
Pension Plan Assets | Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	7.25%
Pension Plan Assets | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocation		63.00%
Pension Plan Assets | Fixed Income Securities and Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocation		37.00%
Postretirement Health Coverage
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations		$ 338,488	$ 346,431	$ 354,739
Expected return on plan assets		7.25%	7.50%	7.70%
Company contributions		$ 15,000	$ 0
Postretirement Health Coverage | Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	7.25%
Postretirement Health Coverage | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocation		69.00%
Postretirement Health Coverage | Fixed Income Securities and Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocation		31.00%