Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Assets
Property, plant and equipment, at cost	$ 6,386,445	$ 6,088,011
Less: accumulated depreciation	1,484,959	1,399,086
Net property, plant and equipment	4,901,486	4,688,925
Current assets:
Cash and cash equivalents	3,712	3,229
Accounts receivable and unbilled revenues, net	109,986	99,146
Inventory, materials and supplies	12,298	12,414
Prepayments and other current assets	11,799	11,802
Assets held for sale	3,606	1,779
Total current assets	141,401	128,370
Regulatory assets	911,455	830,118
Deferred charges and other assets, net	30,903	28,878
Investment in joint venture	8,859	7,716
Goodwill	41,921	33,866
Total assets	6,036,025	5,717,873
Stockholders' equity:
Common stock at $.50 par value, authorized 300,000,000 shares, issued 180,268,028 and 179,363,660 as of September 30, 2016 and December 31, 2015	90,134	89,682
Capital in excess of par value	795,139	773,585
Retained earnings	1,017,261	930,061
Treasury stock, at cost, 2,912,938 and 2,819,569 shares as of September 30, 2016 and December 31, 2015	(70,990)	(68,085)
Accumulated other comprehensive income	656	687
Total stockholders' equity	1,832,200	1,725,930
Long-term debt, excluding current portion	1,748,689	1,743,612
Less: debt issuance costs	22,196	23,165
Long-term debt, excluding current portion, net of debt issuance costs	1,726,493	1,720,447
Commitments and contingencies (See Note 13)
Current liabilities:
Current portion of long-term debt	83,777	35,593
Loans payable	47,990	16,721
Accounts payable	44,073	56,452
Accrued interest	18,236	12,651
Accrued taxes	18,475	21,887
Other accrued liabilities	39,447	49,895
Total current liabilities	251,998	193,199
Deferred credits and other liabilities:
Deferred income taxes and investment tax credits	1,236,516	1,118,923
Customers' advances for construction	93,023	86,934
Regulatory liabilities	250,108	259,507
Other	107,623	100,498
Total deferred credits and other liabilities	1,687,270	1,565,862
Contributions in aid of construction	538,064	512,435
Total liabilities and equity	$ 6,036,025	$ 5,717,873

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Name:	us-gaap_AccountsPayableCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.