CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income		$ 55,505	$ 26,900	$ 44,934
Other comprehensive income:
Unrealized gain on pension plan obligation	[1]	2,075	3,356	3,067
Tax effect of unrealized gain on pension plan obligation		(625)	(1,359)	(1,285)
Unrealized loss on captive insurance collateral		(1,204)
Tax effect of unrealized loss on captive insurance collateral		254
Unrealized gain on interest rate hedge		39
Tax effect of unrealized gain on interest rate hedge		(10)
Total other comprehensive income		529	1,997	1,782
Total comprehensive income		$ 56,034	$ 28,897	$ 46,716

[1] These items are included in the computation of net periodic pension cost. See Note 13 - Employee Benefit Plans.