CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other comprehensive income (loss):
Net unrealized gain (loss) from pension and postretirement plans, tax	$ 0	$ 5,078	$ (3,471)
Reclassification of net unrealized loss on energy derivative instruments during the period, tax	0	0	0
Subsidiaries [Member]
Other comprehensive income (loss):
Net unrealized gain (loss) from pension and postretirement plans, tax	0	9,848	2,004
Reclassification of net unrealized loss on energy derivative instruments during the period, tax	0	0	0
Amortization of treasury interest rate swaps to earnings, tax	$ 0	$ 171	$ 171