Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets
Property, plant and equipment, at cost	$ 11,012,300	$ 8,201,936
Less: accumulated depreciation	1,961,540	1,856,146
Net property, plant and equipment	9,050,760	6,345,790
Current assets:
Cash and cash equivalents	7,227	1,868,922
Accounts receivable, net	152,902	67,137
Unbilled revenues	60,835	40,483
Inventory - materials and supplies	22,660	18,379
Inventory - gas stored	27,424
Prepayments and other current assets	34,194	16,259
Regulatory assets	5,654	2,389
Assets held for sale	1,558	1,558
Total current assets	312,454	2,015,127
Regulatory assets	1,198,340	875,743
Deferred charges and other assets, net	53,636	42,652
Investment in joint venture	5,943	5,984
Funds restricted for construction activity	1,223
Goodwill	2,333,535	63,822
Operating lease right-of-use assets	63,697	12,867
Intangible assets	8,820
Total assets	13,028,408	9,361,985
Stockholders' equity:
Common stock at $0.50 par value, authorized 600,000,000 shares, issued 248,342,756 and 223,871,284 as of June 30, 2020 and December 31, 2019	124,171	111,935
Capital in excess of par value	3,366,695	2,636,555
Retained earnings	1,226,622	1,210,072
Treasury stock, at cost, 3,192,646 and 3,112,565 shares as of June 30, 2020 and December 31, 2019	(81,954)	(77,702)
Total stockholders' equity	4,635,534	3,880,860
Long-term debt, excluding current portion	5,213,370	2,972,349
Less: debt issuance costs	38,769	29,022
Long-term debt, excluding current portion, net of debt issuance costs	5,174,601	2,943,327
Commitments and contingencies (See Note 15)
Current liabilities:
Current portion of long-term debt	87,839	105,051
Loans payable	15,000	25,724
Accounts payable	124,117	74,919
Book overdraft	19,534	10,944
Accrued interest	42,430	29,818
Accrued taxes	30,735	22,775
Regulatory liabilities	28,046	4,612
Other accrued liabilities	100,478	49,618
Total current liabilities	448,179	323,461
Deferred credits and other liabilities:
Deferred income taxes and investment tax credits	1,215,898	936,158
Customers' advances for construction	100,584	95,556
Regulatory liabilities	622,567	512,987
Asset retirement obligations	50,125
Operating lease liabilities	59,338	11,645
Pension and other postretirement benefit liabilities	107,899	69,406
Other	50,405	33,059
Total deferred credits and other liabilities	2,206,816	1,658,811
Contributions in aid of construction	563,278	555,526
Total liabilities and equity	$ 13,028,408	$ 9,361,985