Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets
Property, plant and equipment, at cost	$ 11,321,044	$ 8,201,936
Less: accumulated depreciation	2,060,584	1,856,146
Net property, plant and equipment	9,260,460	6,345,790
Current assets:
Cash and cash equivalents	8,494	1,868,922
Accounts receivable, net	126,774	67,137
Unbilled revenues	62,999	40,483
Inventory - materials and supplies	23,651	18,379
Inventory - gas stored	42,964
Prepayments and other current assets	37,551	16,259
Regulatory assets	8,113	2,389
Assets held for sale	692	1,558
Total current assets	311,238	2,015,127
Regulatory assets	1,369,823	875,743
Deferred charges and other assets, net	51,489	42,652
Investment in joint venture	1,757	5,984
Funds restricted for construction activity	1,243
Goodwill	2,333,627	63,822
Operating lease right-of-use assets	62,022	12,867
Intangible assets	7,829
Total assets	13,399,488	9,361,985
Stockholders' equity:
Common stock at $0.50 par value, authorized 600,000,000 shares, issued 248,457,751 and 223,871,284 as of September 30, 2020 and December 31, 2019	124,228	111,935
Capital in excess of par value	3,372,376	2,636,555
Retained earnings	1,220,790	1,210,072
Treasury stock, at cost, 3,186,771 and 3,112,565 shares as of September 30, 2020 and December 31, 2019	(81,641)	(77,702)
Total stockholders' equity	4,635,753	3,880,860
Long-term debt, excluding current portion	5,190,978	2,972,349
Less: debt issuance costs	38,005	29,022
Long-term debt, excluding current portion, net of debt issuance costs	5,152,973	2,943,327
Commitments and contingencies (See Note 15)
Current liabilities:
Current portion of long-term debt	205,841	105,051
Loans payable	47,185	25,724
Accounts payable	158,197	74,919
Book overdraft	29,110	10,944
Accrued interest	66,728	29,818
Accrued taxes	28,426	22,775
Regulatory liabilities	10,880	4,612
Other accrued liabilities	120,592	49,618
Total current liabilities	666,959	323,461
Deferred credits and other liabilities:
Deferred income taxes and investment tax credits	1,238,328	936,158
Customers' advances for construction	105,613	95,556
Regulatory liabilities	779,117	512,987
Asset retirement obligations	50,927
Operating lease liabilities	57,500	11,645
Pension and other postretirement benefit liabilities	98,209	69,406
Other	48,087	33,059
Total deferred credits and other liabilities	2,377,781	1,658,811
Contributions in aid of construction	566,022	555,526
Total liabilities and equity	$ 13,399,488	$ 9,361,985