Benefit Plans - Additional Disclosures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Company Contributions	$ 0	$ 0
Current plus 1	0
Actual Benefit Payments for the Year Ending: Current	989
Expected Benefit Payments for the Year Ending: Current plus 1	1,600
Expected Benefit Payments for the Year Ending: Current plus 2	1,847
Expected Benefit Payments for the Year Ending: Current plus 3	2,087
Expected Benefit Payments for the Year Ending: Current plus 4	2,254
Expected Benefit Payments for the Year Ending: Current plus 5	2,367
Expected Benefit Payments for the Year Ending: Current plus 6 - 10	11,874
Effect of 1-percentage point increase on total service and interest cost component	380
Effect of 1-percentage point decrease on total service and interest cost components	(328)
Effect of 1-percentage point increase on postretirement benefit obligation	2,528
Effect of 1-percentage point decrease on postretirement benefit obligation	$ (2,239)
Other Postretirement Benefit Plan | Equity securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (in hundredths)	70.00%
Other Postretirement Benefit Plan | Equity securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (in hundredths)	100.00%
Other Postretirement Benefit Plan | Real Estate | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (in hundredths)	0.00%
Other Postretirement Benefit Plan | Real Estate | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (in hundredths)	15.00%
Other Postretirement Benefit Plan | Commodities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (in hundredths)	0.00%
Other Postretirement Benefit Plan | Commodities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (in hundredths)	10.00%
Other Postretirement Benefit Plan | Fixed Income/Cash | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (in hundredths)	0.00%
Other Postretirement Benefit Plan | Fixed Income/Cash | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target asset allocations (in hundredths)	10.00%
Pension and Supplemental Executive Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Company Contributions	$ 10,205	$ 10,908
Current plus 1	12,350
Actual Benefit Payments for the Year Ending: Current	33,934
Expected Benefit Payments for the Year Ending: Current plus 1	34,943
Expected Benefit Payments for the Year Ending: Current plus 2	31,008
Expected Benefit Payments for the Year Ending: Current plus 3	30,981
Expected Benefit Payments for the Year Ending: Current plus 4	31,175
Expected Benefit Payments for the Year Ending: Current plus 5	30,547
Expected Benefit Payments for the Year Ending: Current plus 6 - 10	$ 141,768