CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES
NET INCOME	$ 64,237	$ 67,132
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	38,872	34,435
Recognition, refund and collection of revenue accruals and deferrals — including accrued interest	(16,581)	(12,484)
Deferred income tax expense	160,881	27,823
Allowance for equity funds used during construction	(7,519)	(7,549)
Other	8,550	6,777
Changes in assets and liabilities, exclusive of changes shown separately:
Accounts receivable	(10,778)	(3,826)
Inventory	(1,788)	(72)
Income tax receivable	(141,323)	0
Prepaid and other current assets	(66)	(9,920)
Accounts payable	6,373	(4,855)
Accrued payroll	(6,463)	(7,540)
Accrued interest	(13,001)	(13,172)
Accrued taxes	(10,781)	(11,140)
Other current liabilities	(3,094)	(1,676)
Estimated potential refund related to return on equity complaints	18,900	7,960
Other non-current assets and liabilities, net	1,397	(4,960)
Net cash provided by operating activities	87,816	66,933
CASH FLOWS FROM INVESTING ACTIVITIES
Expenditures for property, plant and equipment	(203,996)	(172,604)
Other	8,754	(5,637)
Net cash used in investing activities	(195,242)	(178,241)
CASH FLOWS FROM FINANCING ACTIVITIES
Borrowings under revolving credit agreements	244,100	349,800
Net issuance of commercial paper, net of discount	211,360	0
Repayments of revolving credit agreements	(331,200)	(222,400)
Dividends on common and restricted stock	(28,585)	(25,220)
Refundable deposits from generators for transmission network upgrades	4,820	143
Repayment of refundable deposits from generators for transmission network upgrades	0	(9,178)
Other	1,293	(464)
Net cash provided by financing activities	101,788	92,681
NET DECREASE IN CASH AND CASH EQUIVALENTS	(5,638)	(18,627)
CASH AND CASH EQUIVALENTS — Beginning of period	13,859	27,741
CASH AND CASH EQUIVALENTS — End of period	$ 8,221	$ 9,114