Benefit Plans - Accumulated Other Comprehensive loss (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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)	$ 44,351	$ 40,061	$ 41,822
Total, pretax effect	44,351	40,061
Tax impact	(11,831)	(10,786)
Ending balance in accumulated other comprehensive loss	32,520	29,275
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)	(1,068)	(1,582)	$ (2,507)
Prior service credit		(51)
Total, pretax effect	(1,068)	(1,633)
Tax impact	285	440
Ending balance in accumulated other comprehensive loss	$ (783)	$ (1,193)