Goodwill and Other Intangible Assets - Goodwill and Accumulated Goodwill Impairment Losses (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Goodwill, gross, beginning balance		$ 2,289,848	$ 2,253,250
Accumulated goodwill impairment losses, beginning balance		(1,281,751)	(1,263,565)
Goodwill, net, beginning balance		1,008,097	989,685
Goodwill acquired during year		220,325	36,598
Impairment losses during year	$ (18,000)	(18,026)	(18,026)
Other			(160)
Goodwill, gross, ending balance		2,510,173	2,289,848
Accumulated goodwill impairment losses, ending balance		(1,281,751)	(1,281,751)
Goodwill, net, ending balance		1,228,422	1,008,097
Operating segments | Northeast segment
Goodwill [Roll Forward]
Goodwill, gross, beginning balance		792,024	792,024
Accumulated goodwill impairment losses, beginning balance		(707,593)	(707,593)
Goodwill, net, beginning balance		84,431	84,431
Goodwill acquired during year		56,400	0
Impairment losses during year			0
Other			0
Goodwill, gross, ending balance		848,424	792,024
Accumulated goodwill impairment losses, ending balance		(707,593)	(707,593)
Goodwill, net, ending balance		140,831	84,431
Operating segments | South segment
Goodwill [Roll Forward]
Goodwill, gross, beginning balance		136,858	100,929
Accumulated goodwill impairment losses, beginning balance		(34,522)	(34,522)
Goodwill, net, beginning balance		102,336	66,407
Goodwill acquired during year		48,300	35,929
Impairment losses during year			0
Other			0
Goodwill, gross, ending balance		185,158	136,858
Accumulated goodwill impairment losses, ending balance		(34,522)	(34,522)
Goodwill, net, ending balance		150,636	102,336
Operating segments | West segment
Goodwill [Roll Forward]
Goodwill, gross, beginning balance		158,992	158,992
Accumulated goodwill impairment losses, beginning balance		(16,633)	(1,812)
Goodwill, net, beginning balance		142,359	157,180
Goodwill acquired during year		51,431	0
Impairment losses during year			(14,821)
Other			0
Goodwill, gross, ending balance		210,423	158,992
Accumulated goodwill impairment losses, ending balance		(16,633)	(16,633)
Goodwill, net, ending balance		193,790	142,359
Operating segments | Midwest segment
Goodwill [Roll Forward]
Goodwill, gross, beginning balance		1,046,652	1,045,983
Accumulated goodwill impairment losses, beginning balance		(435,283)	(435,283)
Goodwill, net, beginning balance		611,369	610,700
Goodwill acquired during year		63,400	669
Impairment losses during year			0
Other			0
Goodwill, gross, ending balance		1,110,052	1,046,652
Accumulated goodwill impairment losses, ending balance		(435,283)	(435,283)
Goodwill, net, ending balance		674,769	611,369
Other
Goodwill [Roll Forward]
Goodwill, gross, beginning balance		155,322	155,322
Accumulated goodwill impairment losses, beginning balance		(87,720)	(84,355)
Goodwill, net, beginning balance		67,602	70,967
Goodwill acquired during year		794	0
Impairment losses during year			(3,205)
Other			(160)
Goodwill, gross, ending balance		156,116	155,322
Accumulated goodwill impairment losses, ending balance		(87,720)	(87,720)
Goodwill, net, ending balance		$ 68,396	$ 67,602