CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
CASH FLOWS FROM OPERATING ACTIVITIES
NET INCOME	$ 134,963	$ 139,468
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	78,241	70,013
Recognition, refund and collection of revenue accruals and deferrals — including accrued interest	(17,991)	(31,867)
Deferred income tax expense	207,964	47,979
Allowance for equity funds used during construction	(16,440)	(15,013)
Other	15,351	10,863
Changes in assets and liabilities, exclusive of changes shown separately:
Accounts receivable	(41,370)	(19,758)
Inventory	(2,049)	1,326
Income tax receivable	(144,573)	0
Prepaid and other current assets	(5,126)	(8,166)
Accounts payable	17,226	(581)
Accrued compensation	(3,110)	(4,497)
Accrued interest	1,426	1,693
Accrued taxes	4,102	2,310
Other current liabilities	(1,670)	(532)
Estimated potential refund related to return on equity complaints	28,803	21,784
Other non-current assets and liabilities, net	1,335	(17,623)
Net cash provided by operating activities	257,082	197,399
CASH FLOWS FROM INVESTING ACTIVITIES
Expenditures for property, plant and equipment	(392,348)	(318,187)
Other	4,008	(5,542)
Net cash used in investing activities	(388,340)	(323,729)
CASH FLOWS FROM FINANCING ACTIVITIES
Issuance of long-term debt	200,000	225,000
Borrowings under revolving credit agreements	461,000	638,500
Net issuance of commercial paper, net of discount	215,801	49,974
Repayments of revolving credit agreements	(509,400)	(729,100)
Repayment of term loan credit agreement	(200,000)	0
Issuance of common stock	10,506	10,704
Dividends on common and restricted stock	(57,278)	(50,467)
Refundable deposits from generators for transmission network upgrades	12,468	981
Repurchase and retirement of common stock	(8,318)	(21,838)
Other	(1,326)	(12,375)
Net cash provided by financing activities	123,453	111,379
NET DECREASE IN CASH AND CASH EQUIVALENTS	(7,805)	(14,951)
CASH AND CASH EQUIVALENTS — Beginning of period	13,859	27,741
CASH AND CASH EQUIVALENTS — End of period	$ 6,054	$ 12,790