Consolidated statements of operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Total revenue	$ 263,042	$ 232,297	$ 184,447
Costs and expenses:
Operating	(103,022)	(98,977)	(81,327)
General and administrative expenses	(23,660)	(23,707)	(23,692)
Insurance expenses	(4,995)	(4,976)	(4,064)
Deferred compensation expense	(2,308)	(3,478)	(2,999)
Depreciation and amortization	(52,535)	(49,793)	(36,188)
Total costs and expenses	(186,520)	(180,931)	(148,270)
Earnings from unconsolidated affiliates	4,894	8,852	7,071
Gain from insurance proceeds	3,351
Loss on disposition of assets		(901)
Operating income	84,767	59,317	43,248
Other expenses:
Interest expense	(36,196)	(31,900)	(10,473)
Amortization of deferred debt issuance costs	(2,657)	(3,037)	(1,221)
Total other expenses	(38,853)	(34,937)	(11,694)
Net earnings	45,914	24,380	31,554
External customers
Revenue:
Total revenue	234,275	211,303	176,079
Affiliate customers
Revenue:
Total revenue	$ 28,767	$ 20,994	$ 8,368