Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities:
Net income	$ 121,918	$ 125,055
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	113,065	102,623
Deferred financing cost amortization	4,246	4,219
Impairment of investment	6,859	0
Stock compensation	1,113	7,093
Deferred income taxes	26,401	21,935
Employee benefit plans	5,656	5,683
Other adjustments, net	3,679	8,991
Changes in certain operating assets and liabilities:
Materials, supplies and fuel	7,503	14,911
Accounts receivable and other current assets	73,302	99,925
Accounts payable and other current liabilities	(63,085)	(107,563)
Regulatory assets - current	21,887	16,116
Regulatory liabilities - current	314	(6,348)
Payment for Pension Benefits	(12,700)	0
Other operating activities, net	(1,152)	(2,861)
Net cash provided by operating activities	309,006	289,779
Investing activities:
Property, plant and equipment additions	(348,313)	(317,686)
Other investing activities	(1,412)	389
Net cash (used in) investing activities	(349,725)	(317,297)
Financing activities:
Dividends paid on common stock	(66,440)	(60,952)
Common stock issued	99,435	71,759
Net (payments) borrowings of short-term debt	(349,500)	(83,120)
Long-term debt - issuances	400,000	400,000
Long-term debt - repayments	(5,727)	(302,871)
Distributions to noncontrolling interest	(8,520)	(9,251)
Other financing activities	(6,474)	(1,948)
Net cash provided by financing activities	62,774	13,617
Net change in cash, restricted cash and cash equivalents	22,055	(13,901)
Cash, restricted cash and cash equivalents at beginning of period	13,658	24,145
Cash, restricted cash and cash equivalents at end of period	35,713	10,244
Supplemental Cash Flow Information [Abstract]
Interest (net of amounts capitalized)	(67,449)	(67,624)
Income taxes	1,896	1,790
Accrued property, plant and equipment purchases at June 30	$ 59,916	$ 83,486