Benefit Plans - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amounts within accumulated other comprehensive loss that had not yet been recognized as components of net periodic benefit cost
Tax impact	$ (11,701)	$ (48,720)	$ (63,040)	$ (57,461)
Pension Benefits
Amounts within accumulated other comprehensive loss that had not yet been recognized as components of net periodic benefit cost
Net actuarial loss (gain)	40,061	41,822	43,547
Total, pretax effect	40,061	41,822
Tax impact	(10,786)	(11,260)
Ending balance in accumulated other comprehensive loss	29,275	30,562
Amounts within accumulated other comprehensive loss expected to be recognized as components of net periodic benefit cost in next year
Amortization of net actuarial loss (gain)	5,753
Total to be recognized in 2020	5,753
Other Benefits
Amounts within accumulated other comprehensive loss that had not yet been recognized as components of net periodic benefit cost
Net actuarial loss (gain)	(1,582)	(2,507)	$ 248
Prior service credit	(51)	(480)
Total, pretax effect	(1,633)	(2,987)
Tax impact	440	804
Ending balance in accumulated other comprehensive loss	(1,193)	$ (2,183)
Amounts within accumulated other comprehensive loss expected to be recognized as components of net periodic benefit cost in next year
Amortization of prior service credit	(51)
Amortization of net actuarial loss (gain)	(103)
Total to be recognized in 2020	$ (154)