Pension Plan and Employee Benefits, 401 (K) Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
401(k) Plan expense	$ 2,063	$ 1,668
Other Subsidiaries
Defined Contribution Plan Disclosure [Line Items]
401(k) Plan expense	$ 402	$ 279