Pension Plan and Employee Benefits - 401 (K) Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Contribution Plan Disclosure [Line Items]
401(k) Plan expense	$ 2,267	$ 2,063
Other Subsidiaries
Defined Contribution Plan Disclosure [Line Items]
401(k) Plan expense	$ 930	$ 402