Business Segment Information - Sales by Geographical Region (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue
Total sales	$ 471,198	$ 382,679	$ 337,339	$ 305,259	$ 379,709	$ 296,212	$ 278,586	$ 248,391	$ 1,496,475	$ 1,202,898	$ 1,107,709
United States
Disaggregation of Revenue
Total sales									956,600	627,800	522,800
United Kingdom
Disaggregation of Revenue
Total sales									218,200	240,700	219,400
Australia
Disaggregation of Revenue
Total sales									163,500	166,700	175,600
Far East/Middle East
Disaggregation of Revenue
Total sales									74,000	86,400	112,700
Other foreign countries
Disaggregation of Revenue
Total sales									$ 84,200	$ 81,300	$ 77,200