Quarterly Financial Information Consolidated statement of cash flows (Details) - USD ($) $ in Thousands		3 Months Ended											6 Months Ended				9 Months Ended				12 Months Ended
		Dec. 31, 2019		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018		Jun. 30, 2019		Jun. 30, 2018		Sep. 30, 2019		Sep. 30, 2018		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Net income (loss)		$ 59,940	[1]	$ 61,492	$ 57,607	$ 57,638		$ 57,303	$ 54,312	$ 52,470	$ 51,432		$ 115,245		$ 103,902		$ 176,737		$ 158,214		$ 236,677		$ 215,517		$ 175,049
Depreciation, amortization and accretion				51,881	51,626	51,580		51,707	51,684	52,083	52,054		103,206		104,137		155,087		155,821		207,396		207,528		207,764
Amortization of deferred financing costs						346					346		692		692		1,038		1,038		1,384		1,384		1,384
Asset write-down charges				0	185	190		249	0	0	344		375		344		375		344		1,050		593		181
Increase (decrease) in accrued interest						9,622					9,622		0		0		9,622		9,622
Increase (decrease) in accounts payable						(32)					(171)		605		449		(3,844)		500		(3,102)		(81)		(1,110)
Increase (decrease) in other liabilities						5,968					6,107		9,473		6,020		15,477		10,826		18,780		15,648		779
Increase (Decrease) in Receivables						1,516					(163)		2,597		231		1,978		(158)		1,887		(1,745)		946
Increase (Decrease) in Other Operating Assets						(3,675)					1,485		(14,277)		(9,155)		(14,256)		(12,505)		13,003		12,003		(9,574)
Net Cash Provided by (Used in) Operating Activities						123,153	[2]				121,056	[2]	217,916	[2]	206,620	[2]	342,214	[2]	323,702	[2]	451,069		426,841	[2]	394,567	[2]
Payments to Acquire Productive Assets						(18,678)					(14,766)		(41,358)		(32,300)		(64,204)		(51,995)		86,610		70,929	[2]	48,312	[2]
Net Cash Provided by (Used in) Investing Activities	[2]					(18,678)					(14,766)		(41,358)		(32,300)		(64,204)		(51,995)		(86,610)		(70,929)		(48,312)
Increase (Decrease) Due from Affiliates						(105,472)					(108,573)		(177,586)		(183,436)		(278,231)		(278,242)		(362,759)	[3]	(367,976)	[2],[3]	(335,034)	[2],[3]
Net Cash Provided by (Used in) Financing Activities	[2]					(105,472)					(108,573)		(177,586)		(183,436)		(278,231)		(278,242)		(362,759)		(367,976)		(335,034)
Cash and Cash Equivalents, Period Increase (Decrease)						(997)					(2,283)		(1,028)		(9,116)		(221)		(6,535)		1,700		(12,064)		11,221
Cash and cash equivalents		$ 20,407		18,486	17,679	17,710		18,707	24,236	21,655	28,488		17,679		21,655		18,486		24,236		$ 20,407		18,707		30,771		$ 19,550
Restatement Adjustment [Member]
Net income (loss)				14,172	13,500	12,907		12,529	11,450	11,208	10,671		26,407		21,879		40,579		33,329				45,858		41,145
Depreciation, amortization and accretion				(736)	(736)	(736)		(555)	(604)	(604)	(604)		(1,472)		(1,208)		(2,208)		(1,812)				(2,367)		(2,710)
Increase (decrease) in other liabilities						2,230					1,143		8,565		3,028		13,860		7,817				11,302		(1,185)
Net Cash Provided by (Used in) Operating Activities	[2]					14,401					11,210		33,500		23,699		52,231		39,334				54,793		37,250
Payments to Acquire Productive Assets						0					0		0		0		0		0				0	[2]	0	[2]
Net Cash Provided by (Used in) Investing Activities						0	[2]				0	[2]	0	[2]	0	[2]	0	[2]	0	[2]			0		0
Increase (Decrease) Due from Affiliates						(14,401)					(11,210)		(33,500)		(23,699)		(52,231)		(39,334)				(54,793)	[2]	(37,250)	[2]
Net Cash Provided by (Used in) Financing Activities						(14,401)	[2]				(11,210)	[2]	(33,500)	[2]	(23,699)	[2]	(52,231)	[2]	(39,334)	[2]			(54,793)		(37,250)
Cash and Cash Equivalents, Period Increase (Decrease)						0					0		0		0		0		0				0		0
Cash and cash equivalents				0	0	0		0	0	0	0		0		0		0		0				0		0		0
Other Adjustment [Member]
Net income (loss)				48	47	46		45	45	44	43		93		87		141		132				177		133
Depreciation, amortization and accretion				(48)	(47)	(46)		(45)	(45)	(44)	(43)		(93)		(87)		(141)		(132)				(177)		(133)
Increase (decrease) in other liabilities						0					0		0		0		0		0				0		0
Net Cash Provided by (Used in) Operating Activities	[2]					0					0		0		0		0		0				0		0
Payments to Acquire Productive Assets						67					55		106		114		199		192				(221)	[2]	(1,239)	[2]
Net Cash Provided by (Used in) Investing Activities						67	[2]				55	[2]	106	[2]	114	[2]	199	[2]	192	[2]			221		1,239
Increase (Decrease) Due from Affiliates						(67)					(55)		(106)		(114)		(199)		(192)				(221)	[2]	(1,239)	[2]
Net Cash Provided by (Used in) Financing Activities						(67)	[2]				(55)	[2]	(106)	[2]	(114)	[2]	(199)	[2]	(192)	[2]			(221)		(1,239)
Cash and Cash Equivalents, Period Increase (Decrease)						0					0		0		0		0		0				0		0
Cash and cash equivalents				0	0	0		0	0	0	0		0		0		0		0				0		0		0
Previously Reported [Member]
Net income (loss)				47,272	44,060	44,685		44,729	42,817	41,218	40,718		88,745		81,936		136,017		124,753				169,482		133,771
Depreciation, amortization and accretion				52,665	52,409	52,362		52,307	52,333	52,731	52,701		104,771		105,432		157,436		157,765				210,072		210,607
Increase (decrease) in other liabilities						3,738					4,964		908		2,992		1,617		3,009				4,346		1,964
Net Cash Provided by (Used in) Operating Activities	[2]					108,752					109,846		184,416		182,921		289,983		284,368				372,048		357,317
Payments to Acquire Productive Assets						(18,745)					(14,821)		(41,464)		(32,414)		(64,403)		(52,187)				71,150	[2]	49,551	[2]
Net Cash Provided by (Used in) Investing Activities						(18,745)	[2]				(14,821)	[2]	(41,464)	[2]	(32,414)	[2]	(64,403)	[2]	(52,187)	[2]			(71,150)		(49,551)
Increase (Decrease) Due from Affiliates						(91,004)					(97,308)		(143,980)		(159,623)		(225,801)		(238,716)				(312,962)	[2]	(296,545)	[2]
Net Cash Provided by (Used in) Financing Activities						(91,004)	[2]				(97,308)	[2]	(143,980)	[2]	(159,623)	[2]	(225,801)	[2]	(238,716)	[2]			(312,962)		(296,545)
Cash and Cash Equivalents, Period Increase (Decrease)						(997)					(2,283)		(1,028)		(9,116)		(221)		(6,535)				(12,064)		11,221
Cash and cash equivalents				$ 18,486	$ 17,679	$ 17,710		$ 18,707	$ 24,236	$ 21,655	$ 28,488		$ 17,679		$ 21,655		$ 18,486		$ 24,236				$ 18,707		$ 30,771		$ 19,550

[1] The sum of quarterly information may not agree to year-to-date information due to rounding. Resta

[2] The Company receives no cash from, and is not party to, the CCIC transactions described in note 2. Such transactions, however, are reflected on the cash flow statement for GAAP purposes as if an amount equal to the lease component for such transactions had been received by the Company, and as such, the amounts have been recorded as fixed assets (in the form of permanent improvements) and deferred revenues.

[3] The Company receives no cash from, and is not party to, the CCIC transactions described in note 2.