Reportable Segments (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Mar. 31, 2015 segment	Dec. 31, 2014	Mar. 31, 2014	Mar. 31, 2015 segment	Mar. 31, 2014	Sep. 30, 2014
Summarized financial information concerning the Company's reportable segments
Number of reportable segments	3us-gaap_NumberOfReportableSegments			3us-gaap_NumberOfReportableSegments
Revenue	$ 4,506,197us-gaap_SalesRevenueServicesNet		$ 1,872,224us-gaap_SalesRevenueServicesNet	$ 8,716,665us-gaap_SalesRevenueServicesNet	$ 3,826,099us-gaap_SalesRevenueServicesNet
Gross profit	103,312us-gaap_GrossProfit		87,407us-gaap_GrossProfit	238,042us-gaap_GrossProfit	165,605us-gaap_GrossProfit
Equity in (losses) earnings of joint ventures	24,628		7,436	48,552	43,519
General and administrative expenses	(29,797)us-gaap_GeneralAndAdministrativeExpense		(26,449)us-gaap_GeneralAndAdministrativeExpense	(64,135)us-gaap_GeneralAndAdministrativeExpense	(50,294)us-gaap_GeneralAndAdministrativeExpense
Acquisition and integration expenses	(91,599)			(230,062)
Operating income	6,544us-gaap_OperatingIncomeLoss		68,394us-gaap_OperatingIncomeLoss	(7,603)us-gaap_OperatingIncomeLoss	158,830us-gaap_OperatingIncomeLoss
Gross profit as a % of revenue		2.30%	4.70%	2.70%	4.30%
Total Assets	14,016,005us-gaap_Assets			14,016,005us-gaap_Assets		6,123,377us-gaap_Assets
Corporate
Summarized financial information concerning the Company's reportable segments
General and administrative expenses	(29,800)		(26,400)	(64,100)	(50,300)
Acquisition and integration expenses	(91,600)			(230,100)
Operating income	(121,400)		(26,400)	(294,200)	(50,300)
Total Assets	603,900			603,900		365,000
Design and Consulting Services
Summarized financial information concerning the Company's reportable segments
Revenue	2,035,900		1,306,900	3,927,600	2,608,300
Gross profit	53,000		76,400	99,400	130,300
Equity in (losses) earnings of joint ventures	(1,400)		(400)		32,300
Operating income	51,600		76,000	99,400	162,600
Gross profit as a % of revenue	2.60%		5.80%	2.50%	5.00%
Total Assets	7,179,600			7,179,600		4,064,500
Construction Services
Summarized financial information concerning the Company's reportable segments
Revenue	1,641,100		338,900	3,175,200	767,600
Gross profit	2,500		7,000	37,800	11,000
Equity in (losses) earnings of joint ventures	4,700		700	10,600	2,100
Operating income	7,200		7,700	48,400	13,100
Gross profit as a % of revenue	0.20%		2.10%	1.20%	1.40%
Total Assets	3,117,600			3,117,600		1,256,400
Management Services
Summarized financial information concerning the Company's reportable segments
Revenue	829,200		226,400	1,613,900	450,200
Gross profit	47,700		4,000	100,800	24,300
Equity in (losses) earnings of joint ventures	21,400		7,100	38,000	9,100
Operating income	69,100		11,100	138,800	33,400
Gross profit as a % of revenue	5.80%		1.80%	6.20%	5.40%
Total Assets	$ 3,114,900			$ 3,114,900		$ 437,500

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