Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets
Property, plant and equipment, at cost	$ 7,998,861	$ 7,648,469
Less: accumulated depreciation	1,801,909	1,718,143
Net property, plant and equipment	6,196,952	5,930,326
Current assets:
Cash and cash equivalents	2,030,568	3,627
Accounts receivable, net	75,573	65,825
Unbilled revenues	41,406	35,400
Inventory, materials and supplies	17,035	15,844
Prepayments and other current assets	12,753	23,337
Assets held for sale	1,558	3,139
Total current assets	2,178,893	147,172
Regulatory assets	851,061	788,076
Deferred charges and other assets, net	42,227	39,237
Investment in joint venture	6,253	6,959
Goodwill	52,701	52,726
Operating lease right-of-use assets	12,883
Total assets	9,340,970	6,964,496
Stockholders' equity:
Common stock at $0.50 par value, authorized 300,000,000 shares, issued 218,940,681 and 181,151,827 as of September 30, 2019 and December 31, 2018	109,471	90,576
Capital in excess of par value	2,633,193	820,378
Retained earnings	1,197,600	1,174,245
Treasury stock, at cost, 3,112,565 and 3,060,206 shares as of September 30, 2019 and December 31, 2018	(77,702)	(75,835)
Total stockholders' equity	3,862,562	2,009,364
Long-term debt, excluding current portion	2,933,905	2,419,115
Less: debt issuance costs	35,607	20,651
Long-term debt, excluding current portion, net of debt issuance costs	2,898,298	2,398,464
Commitments and contingencies (See Note 15)
Current liabilities:
Current portion of long-term debt	178,116	144,545
Loans payable	10,000	15,449
Accounts payable	57,589	77,331
Book overdraft	5,068	8,950
Accrued interest	38,251	23,300
Accrued taxes	17,568	22,234
Interest rate swap agreements		59,779
Other accrued liabilities	45,531	47,389
Total current liabilities	352,123	398,977
Deferred credits and other liabilities:
Deferred income taxes and investment tax credits	909,232	845,403
Customers' advances for construction	104,393	93,343
Regulatory liabilities	520,213	531,027
Operating lease liabilities	11,700
Other	100,025	97,182
Total deferred credits and other liabilities	1,645,563	1,566,955
Contributions in aid of construction	582,424	590,736
Total liabilities and equity	$ 9,340,970	$ 6,964,496