BUSINESS SEGMENT INFORMATION - Geographic information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Business segment financial data
Sales	$ 406,588	$ 375,240	$ 366,024	$ 313,813	$ 425,917	$ 347,806	$ 338,834	$ 318,488	$ 1,461,665	$ 1,431,045	$ 1,398,352
Long-lived assets, net	101,000				78,700				101,000	78,700	65,400
United States
Business segment financial data
Sales									827,000	765,000	749,900
Long-lived assets, net	86,300				65,800				86,300	65,800	49,800
United Kingdom
Business segment financial data
Sales									243,000	282,400	294,400
Long-lived assets, net	5,300				8,600				5,300	8,600	9,300
Canada
Business segment financial data
Sales									44,600	17,600	9,000
Australia
Business segment financial data
Sales									154,000	164,600	161,900
Middle East
Business segment financial data
Sales									71,000	67,700	42,000
Far East
Business segment financial data
Sales									57,400	55,300	76,600
Other foreign countries
Business segment financial data
Sales									64,700	78,400	64,600
Long-lived assets, net	$ 9,400				$ 4,300				$ 9,400	$ 4,300	$ 6,300