Pension Plan and Employee Benefits - 401 (K) Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Contribution Plan Disclosure [Line Items]
401(k) Plan expense	$ 2,120	$ 1,898	$ 4,880	$ 5,154
Other Subsidiaries
Defined Contribution Plan Disclosure [Line Items]
401(k) Plan expense	$ 946	$ 832	$ 2,326	$ 2,495