Reportable Segments (Details) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) segment	Jun. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)
Summarized financial information concerning the Company's reportable segments
Number of reportable segments \| segment			4
Revenue	$ 4,561,467	$ 4,408,782	$ 13,347,014	$ 13,087,729
Cost of revenue	4,386,291	4,237,439	12,833,421	12,592,084
Gross profit	175,176	171,343	513,593	495,645
Equity in earnings of joint ventures	66,458	18,513	109,667	82,792
General and administrative expenses	(33,944)	(28,863)	(96,427)	(86,957)
Acquisition and integration expenses		(50,678)	(35,409)	(142,427)
Gain (loss) on disposal activities			572	(42,589)
Operating income	$ 207,690	$ 110,315	$ 491,996	$ 306,464
Gross profit as a % of revenue	3.80%	3.90%	3.80%	3.80%
Segment assets	$ 13,836,242		$ 13,836,242		$ 13,669,936
Corporate
Summarized financial information concerning the Company's reportable segments
General and administrative expenses	(31,900)	$ (27,100)	(89,900)	$ (82,300)
Acquisition and integration expenses		(50,700)	(35,400)	(142,400)
Operating income	(31,900)	(77,800)	(125,300)	(224,700)
Segment assets	571,100		571,100		586,200
DCS
Summarized financial information concerning the Company's reportable segments
Revenue	1,863,500	1,920,600	5,571,800	5,748,900
Gross profit	91,200	122,900	292,500	299,400
Equity in earnings of joint ventures	2,500	1,000	12,600	6,200
Gain (loss) on disposal activities			600
Operating income	$ 93,700	$ 123,900	$ 305,700	$ 305,600
Gross profit as a % of revenue	4.90%	6.40%	5.20%	5.20%
Segment assets	$ 6,691,100		$ 6,691,100		6,655,700
CS
Summarized financial information concerning the Company's reportable segments
Revenue	1,841,700	$ 1,650,800	5,324,600	$ 4,842,500
Gross profit	26,200	7,700	60,400	23,000
Equity in earnings of joint ventures	7,000	3,500	16,600	8,900
Gain (loss) on disposal activities				(42,600)
Operating income	$ 33,200	$ 11,200	$ 77,000	$ (10,700)
Gross profit as a % of revenue	1.40%	0.50%	1.10%	0.50%
Segment assets	$ 3,744,500		$ 3,744,500		3,556,200
CS \| Restatement Adjustment
Summarized financial information concerning the Company's reportable segments
Revenue		$ (33,000)		$ (99,300)
Cost of revenue		(31,600)		(94,500)
MS
Summarized financial information concerning the Company's reportable segments
Revenue	856,300	837,400	2,450,600	2,496,300
Gross profit	57,800	40,700	160,700	173,200
Equity in earnings of joint ventures	8,600	14,000	32,100	67,700
Operating income	$ 66,400	$ 54,700	$ 192,800	$ 240,900
Gross profit as a % of revenue	6.70%	4.90%	6.60%	6.90%
Segment assets	$ 2,638,700		$ 2,638,700		2,692,700
MS \| Restatement Adjustment
Summarized financial information concerning the Company's reportable segments
Revenue		$ 33,000		$ 99,300
Cost of revenue		31,600		94,500
ACAP
Summarized financial information concerning the Company's reportable segments
Equity in earnings of joint ventures	48,400		48,400
General and administrative expenses	(2,100)	(1,600)	(6,600)	(4,600)
Operating income	46,300	$ (1,600)	41,800	$ (4,600)
Segment assets	$ 190,800		$ 190,800		$ 179,100

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