Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net income	$ 24,694	$ 17,693	$ 121,918	$ 125,055
Other comprehensive income (loss), net of tax:
Benefit plan liability adjustments - net gain (net of tax of $0,$0, $(17) and $0, respectively)	0	0	55	0
Reclassification adjustments of benefit plan liability - prior service cost (net of tax of $6, $5, $13 and $10, respectively)	(19)	(15)	(42)	(29)
Reclassification adjustments of benefit plan liability - net gain (net of tax of $(182), $(52), $(277) and $(105), respectively)	415	169	917	336
Other comprehensive income, net of tax	948	232	2,221	689
Comprehensive income	25,642	17,925	124,139	125,744
Net Income (Loss) Attributable to Noncontrolling Interest	3,728	3,110	7,778	6,664
Comprehensive income available for common stock	21,914	14,815	116,361	119,080
Benefit plan liability adjustments - net gain (loss) (tax) benefit	0	0	(17)	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, Tax	6	5	13	10
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	(182)	(52)	(277)	(105)
Interest rate swaps
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses	543	541	1,086	1,091
Reclassification of net realized gains/losses, (tax) benefit	(170)	(172)	(340)	(335)
Commodity Contract
Other comprehensive income (loss), net of tax:
Reclassification of net realized (gains) losses	54	(64)	425	(490)
Net unrealized gains (losses) on commodity derivatives (net of tax of $14, $119, $68 and $65, respectively)	(45)	(399)	(220)	(219)
Reclassification of net realized gains/losses, (tax) benefit	(16)	19	(131)	147
Net unrealized gains/losses on commodity derivatives, (tax) benefit	$ 14	$ 119	$ 68	$ 65