Supplemental Guarantor / Non-Guarantor Financial Information Condensed Consolidating Statement of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues [Abstract]
Affiliates	$ 101,428	$ 89,025
Third parties	27,456	16,609
Total revenues	128,884	105,634
Operating costs and expenses [Abstract]
Operations (exclusive of depreciation and amortization)	36,202	32,489
Depreciation and amortization	25,142	18,777
General and administrative	3,122	2,634
Total operating costs and expenses	64,466	53,900
Operating Income (Loss)	64,418	51,734
Equity in earnings of subsidiaries	0	0
Equity in earnings of equity method investments	1,279	1,840
Interest expense	(17,581)	(13,539)
Interest income	515	102
Loss on early extinguishment of debt	0	(12,225)
Gain on sale of assets and other	86	73
Nonoperating Income (Expense)	(15,701)	(23,749)
Income before income taxes	48,717	27,985
State income tax benefit (expense)	(82)	(106)
Net income	48,635	27,879
Allocation of net income attributable to noncontrolling interests	(2,467)	(2,316)
Net income attributable to the partners	46,168	25,563
Other comprehensive income	0	63
Comprehensive income attributable to the partners	46,168	25,626
Parent Company [Member]
Revenues [Abstract]
Affiliates	0	0
Third parties	0	0
Total revenues	0	0
Operating costs and expenses [Abstract]
Operations (exclusive of depreciation and amortization)	0	0
Depreciation and amortization		0
General and administrative	1,280	1,155
Total operating costs and expenses	1,280	1,155
Operating Income (Loss)	(1,280)	(1,155)
Equity in earnings of subsidiaries	65,052	45,283
Equity in earnings of equity method investments	0	0
Interest expense	(17,649)	(6,340)
Interest income	0	0
Loss on early extinguishment of debt		(12,225)
Gain on sale of assets and other	45	0
Nonoperating Income (Expense)	47,448	26,718
Income before income taxes	46,168	25,563
State income tax benefit (expense)	0	0
Net income	46,168	25,563
Allocation of net income attributable to noncontrolling interests	0	0
Net income attributable to the partners	46,168	25,563
Other comprehensive income	0	63
Comprehensive income attributable to the partners	46,168	25,626
Guarantor Subsidiaries [Member]
Revenues [Abstract]
Affiliates	94,291	80,776
Third parties	19,978	11,003
Total revenues	114,269	91,779
Operating costs and expenses [Abstract]
Operations (exclusive of depreciation and amortization)	32,664	29,092
Depreciation and amortization	21,001	14,853
General and administrative	1,842	1,479
Total operating costs and expenses	55,507	45,424
Operating Income (Loss)	58,762	46,355
Equity in earnings of subsidiaries	5,212	4,901
Equity in earnings of equity method investments	1,279	1,840
Interest expense	68	(7,199)
Interest income	515	102
Loss on early extinguishment of debt		0
Gain on sale of assets and other	28	72
Nonoperating Income (Expense)	7,102	(284)
Income before income taxes	65,864	46,071
State income tax benefit (expense)	(82)	(106)
Net income	65,782	45,965
Allocation of net income attributable to noncontrolling interests	(730)	(682)
Net income attributable to the partners	65,052	45,283
Other comprehensive income	0	63
Comprehensive income attributable to the partners	65,052	45,346
Non-Guarantor Subsidiaries [Member]
Revenues [Abstract]
Affiliates	7,137	8,249
Third parties	7,478	5,606
Total revenues	14,615	13,855
Operating costs and expenses [Abstract]
Operations (exclusive of depreciation and amortization)	3,538	3,397
Depreciation and amortization	4,141	3,924
General and administrative	0	0
Total operating costs and expenses	7,679	7,321
Operating Income (Loss)	6,936	6,534
Equity in earnings of subsidiaries	0	0
Equity in earnings of equity method investments	0	0
Interest expense	0	0
Interest income	0	0
Loss on early extinguishment of debt		0
Gain on sale of assets and other	13	1
Nonoperating Income (Expense)	13	1
Income before income taxes	6,949	6,535
State income tax benefit (expense)	0	0
Net income	6,949	6,535
Allocation of net income attributable to noncontrolling interests	(1,737)	(1,634)
Net income attributable to the partners	5,212	4,901
Other comprehensive income	0	0
Comprehensive income attributable to the partners	5,212	4,901
Consolidation, Eliminations [Member]
Revenues [Abstract]
Affiliates	0	0
Third parties	0	0
Total revenues	0	0
Operating costs and expenses [Abstract]
Operations (exclusive of depreciation and amortization)	0	0
Depreciation and amortization	0	0
General and administrative	0	0
Total operating costs and expenses	0	0
Operating Income (Loss)	0	0
Equity in earnings of subsidiaries	(70,264)	(50,184)
Equity in earnings of equity method investments	0	0
Interest expense	0	0
Interest income	0	0
Loss on early extinguishment of debt		0
Gain on sale of assets and other	0	0
Nonoperating Income (Expense)	(70,264)	(50,184)
Income before income taxes	(70,264)	(50,184)
State income tax benefit (expense)	0	0
Net income	(70,264)	(50,184)
Allocation of net income attributable to noncontrolling interests	0	0
Net income attributable to the partners	(70,264)	(50,184)
Other comprehensive income	0	(63)
Comprehensive income attributable to the partners	$ (70,264)	$ (50,247)