CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net unrealized gain (loss) from pension and postretirement plans, net of tax	$ (115)	$ (100)	$ 359	$ (200)
Reclassification of net unrealized loss on energy derivative instruments during the period, net of tax	0	0	0	0
Subsidiaries [Member]
Net unrealized gain (loss) from pension and postretirement plans, net of tax	1,143	1,260	2,875	2,520
Reclassification of net unrealized loss on energy derivative instruments during the period, net of tax	0	0	0	0
Amortization of treasury interest rate swaps to earnings, net of tax	$ 43	$ 43	$ 86	$ 86