Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets
Property, plant and equipment, at cost	$ 10,795,110	$ 8,201,936
Less: accumulated depreciation	1,905,274	1,856,146
Net property, plant and equipment	8,889,836	6,345,790
Current assets:
Cash and cash equivalents	31,848	1,868,922
Accounts receivable, net	179,572	67,137
Unbilled revenues	83,979	40,483
Inventory - materials and supplies	22,224	18,379
Inventory - gas stored	11,693
Prepayments and other current assets	32,024	16,259
Regulatory assets	5,110	2,389
Assets held for sale	1,558	1,558
Total current assets	368,008	2,015,127
Regulatory assets	1,186,102	875,743
Deferred charges and other assets, net	61,754	42,652
Investment in joint venture	5,473	5,984
Funds restricted for construction activity	1,223
Goodwill	2,351,526	63,822
Operating lease right-of-use assets	65,064	12,867
Total assets	12,928,986	9,361,985
Stockholders' equity:
Common stock at $0.50 par value, authorized 300,000,000 shares, issued 248,234,603 and 223,871,284 as of March 31, 2020 and December 31, 2019	124,117	111,935
Capital in excess of par value	3,361,586	2,636,555
Retained earnings	1,209,501	1,210,072
Treasury stock, at cost, 3,194,287 and 3,112,565 shares as of March 31, 2020 and December 31, 2019	(82,041)	(77,702)
Total stockholders' equity	4,613,163	3,880,860
Long-term debt, excluding current portion	4,757,427	2,972,349
Less: debt issuance costs	28,393	29,022
Long-term debt, excluding current portion, net of debt issuance costs	4,729,034	2,943,327
Commitments and contingencies (See Note 15)
Current liabilities:
Current portion of long-term debt	115,011	105,051
Loans payable	381,005	25,724
Accounts payable	115,611	74,919
Book overdraft		10,944
Accrued interest	51,871	29,818
Accrued taxes	41,876	22,775
Regulatory liabilities	31,663	4,612
Other accrued liabilities	90,337	49,618
Total current liabilities	827,374	323,461
Deferred credits and other liabilities:
Deferred income taxes and investment tax credits	1,192,900	936,158
Customers' advances for construction	99,447	95,556
Regulatory liabilities	640,503	512,987
Asset retirement obligations	49,272
Operating lease liabilities	60,970	11,645
Pension and other postretirement benefit liabilities	110,018	69,406
Other	48,864	33,059
Total deferred credits and other liabilities	2,201,974	1,658,811
Contributions in aid of construction	557,441	555,526
Total liabilities and equity	$ 12,928,986	$ 9,361,985