Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 82,079	$ 111,082	$ 421,585
Adjustments to reconcile net income to net cash provided by operating activities -
Depreciation, depletion and amortization	252,480	222,196	150,140
Provision for leased items no longer in use	12,589	0	0
Gain on sale of assets	(40,311)	0	0
Gain on basis step up on historical interest	0	0	(332,380)
Amortization and write-off of debt issuance costs and premium or discount	13,103	10,138	10,881
Amortization of unearned income and initial direct costs on direct financing leases	(13,747)	(14,395)	(14,979)
Payments received under direct financing leases	20,668	20,672	20,664
Equity in earnings of investments in equity investees	(51,046)	(47,944)	(54,450)
Cash distributions of earnings of equity investees	62,618	65,867	71,823
Non-cash effect of equity-based compensation plans	(5,775)	6,558	5,014
Deferred and other tax benefits	(4,060)	2,142	2,960
Unrealized (gains) losses on derivative transactions	10,943	1,287	(1,009)
Other, net	(10,839)	11,385	3,915
Net changes in components of operating assets and liabilities, net of acquisitions (See Note 15)	10,156	(90,650)	5,372
Net cash provided by operating activities	338,858	298,338	289,536
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments to acquire fixed and intangible assets	(250,593)	(463,100)	(495,774)
Cash distributions received from equity investees—return of investment	20,280	21,353	25,645
Investments in equity investees	(4,647)	0	(3,045)
Acquisitions	(1,325,759)	(25,394)	(1,520,299)
Contributions in aid of construction costs	124	13,374	3,179
Proceeds from asset sales	85,722	3,609	2,811
Other, net	0	(151)	(1,976)
Net cash used in investing activities	(1,474,873)	(450,309)	(1,989,459)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings on senior secured credit facility	1,458,700	1,115,800	1,525,050
Repayments on senior secured credit facility	(1,637,700)	(952,600)	(960,450)
Proceeds from issuance of senior unsecured notes	1,000,000	0	1,139,718
Proceeds from issuance of Class A convertible preferred units, net	726,419	0	0
Repayment of senior unsecured notes	(204,830)	0	(350,000)
Debt issuance costs	(25,913)	(1,578)	(28,901)
Issuance of common units for cash, net	140,513	298,020	633,759
Contributions (distributions) from (to) noncontrolling interests	2,770	236	(960)
Distributions to common unitholders	(321,875)	(310,039)	(256,389)
Other, net	(57)	(1,734)	(471)
Net cash provided by financing activities	1,138,027	148,105	1,701,356
Net increase (decrease) in cash and cash equivalents	2,012	(3,866)	1,433
Cash and cash equivalents at beginning of period	7,029	10,895	9,462
Cash and cash equivalents at end of period	$ 9,041	$ 7,029	$ 10,895