STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Retained Earnings [Member]	Owner's Net Investment [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]
Common Stock, Dividends, Declared, Annualized Basis	$ 0.84
Shares Issued, beginning balance at Dec. 31, 2013						100
Equity, beginning balance at Dec. 31, 2013	$ 1,239,023	$ 0	$ 1,239,023	$ 0	$ 0	$ 0	$ 0
Net income	109,790	84,214	25,576	0	0	0	0
Other comprehensive loss	(1,781)	0	0	(1,781)	0	0	0
Net transfers from ONEOK	481,086	0	484,479	(3,393)	0	0	0
Reclassification of Owner's investment to paid-in capital	0	0	(1,749,078)	0	0	$ 0	1,749,078
Net issuance of common stock at the separation, Shares						51,941,136
Issuance of common stock at the separation, value	0	0	0	0	0	$ 520	(520)
Common stock issued, shares						142,623
Common stock issued, value	9,615	0	0	0	0	$ 1	9,614
Common stock dividends	(43,696)	(44,320)	0	0	0	$ 0	624
Shares Issued, ending balance at Dec. 31, 2014						52,083,859
Equity, ending balance at Dec. 31, 2014	$ 1,794,037	39,894	0	(5,174)	0	$ 521	1,758,796
Common Stock, Dividends, Declared, Annualized Basis	$ 1.20
Net income	$ 119,030	119,030	0	0	0	0	0
Other comprehensive loss	773	0	0	773	0	0	0
Repurchase of common stock	(24,122)	0	0	0	(24,122)	$ 0	0
Common stock issued, shares						514,146
Common stock issued, value	14,663	0	0	0	9,631	$ 5	5,027
Common stock dividends	(62,826)	(63,878)	0	0	0	$ 0	1,052
Shares Issued, ending balance at Dec. 31, 2015						52,598,005
Equity, ending balance at Dec. 31, 2015	$ 1,841,555	95,046	0	(4,401)	(14,491)	$ 526	1,764,875
Common Stock, Dividends, Declared, Annualized Basis	$ 1.40
Net income	$ 140,095	140,095	0	0	0	0	0
Other comprehensive loss	(314)	0	0	(314)	0	0	0
Repurchase of common stock	(24,066)	0	0	0	(24,066)	$ 0	0
Common stock issued, shares						0
Common stock issued, value	4,219	0	0	0	20,431	$ 0	(16,212)
Common stock dividends	(73,209)	(74,120)	0	0	0	$ 0	911
Shares Issued, ending balance at Dec. 31, 2016						52,598,005
Equity, ending balance at Dec. 31, 2016	$ 1,888,280	$ 161,021	$ 0	$ (4,715)	$ (18,126)	$ 526	$ 1,749,574