Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenues	$ 279,254	$ 269,681
Costs and expenses:
Service costs (exclusive of depreciation and amortization)	115,399	113,042
Selling, general and administrative expenses	47,512	47,708
Management fee expense	6,600	6,000
Depreciation and amortization	36,205	37,436
Operating income	73,538	65,495
Interest expense, net	(14,117)	(17,133)
Gain on derivatives, net		1,467
Other expense, net	(304)	(321)
Net income	59,117	49,508
Dividend to preferred members (Note 7)	(4,500)	(4,500)
Net income applicable to member	$ 54,617	$ 45,008