Amount of sublease rentals anticipated to be received during the next five fiscal years.

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The percentage of employees covered by collective bargaining agreements as of the balance sheet date when it serves as a benchmark in a concentration of risk calculation.

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The aggregate cost of goods produced and sold and services rendered during the reporting period.

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The noncurrent portion of deferred revenue amount as of balance sheet date. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized, and is not expected to be recognized in the next twelve months. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

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The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

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The net result for the period of deducting operating expenses from operating revenues.

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Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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The amount of revenue recognized for the period under subleasing arrangements.

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Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Commitments and contingencies (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Apr. 30, 2012
Performance bonds
Performance bond commitments	$ 27,300								$ 27,300
Operating Lease expense									67,100	$ 61,800	$ 49,000
Operating sublease income									500
Minimum future lease commitments under leases
2016	70,892								70,892
2017	56,876								56,876
2018	40,892								40,892
2019	29,693								29,693
2020	18,505								18,505
Thereafter	4,919								4,919
Total minimum lease payments	221,777								221,777
Deferred revenue recorded	52,954				$ 32,257				52,954	32,257
Additional revenue recognized from significant contract	578,683	$ 572,301	$ 481,794	$ 467,043	435,406	$ 419,899	$ 439,015	$ 406,592	2,099,821	1,700,912	1,331,279
Additional cost recognized for significant contract									1,587,104	1,248,789	945,246
Operating profit	61,527	$ 71,067	$ 62,007	$ 65,231	$ 51,808	$ 55,223	$ 64,980	$ 53,297	$ 259,832	$ 225,308	185,155
Percentage of employees covered by collective bargaining agreements									18.00%
Sublease income	1,200								$ 1,200
PSI \| Loss contract
Minimum future lease commitments under leases
Deferred revenue recorded												$ 15,100
Additional revenue recognized from significant contract											16,000
Additional cost recognized for significant contract											5,100
Operating profit											$ 10,900
Office space
Minimum future lease commitments under leases
2016	66,172								66,172
2017	52,745								52,745
2018	37,475								37,475
2019	27,004								27,004
2020	16,971								16,971
Thereafter	4,919								4,919
Total minimum lease payments	205,286								205,286
Equipment
Minimum future lease commitments under leases
2016	4,720								4,720
2017	4,131								4,131
2018	3,417								3,417
2019	2,689								2,689
2020	1,534								1,534
Total minimum lease payments	$ 16,491								$ 16,491