CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands		3 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income		$ 2,315	$ 30,182
Other comprehensive income:
Unrealized gain on pension plan obligation	[1]	454	448
Tax effect of unrealized gain on pension plan obligation		(124)	(135)
Unrealized gain on investments		389
Tax effect of unrealized gain on investments		(82)
Unrealized loss on interest rate hedges		(745)
Tax effect of unrealized loss on interest rate hedges		197
Total other comprehensive income		89	313
Total comprehensive income		$ 2,404	$ 30,495

[1] This item is included in the computation of net periodic pension cost.