Pension Plan and Employee Benefits - 401 (K) Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Contribution Plan Disclosure [Line Items]
401(k) Plan expense	$ 1,792	$ 1,229	$ 4,059	$ 3,292
Other Subsidiaries
Defined Contribution Plan Disclosure [Line Items]
401(k) Plan expense	$ 821	$ 209	$ 1,752	$ 611