Pension Plan and Employee Benefits - 401 (K) Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Contribution Plan Disclosure [Line Items]
401(k) Plan expense	$ 2,356	$ 2,077	$ 7,509	$ 6,136
Other Subsidiaries
Defined Contribution Plan Disclosure [Line Items]
401(k) Plan expense	$ 996	$ 873	$ 3,491	$ 2,625