Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 44,265	$ 23,351
Other comprehensive income:
Net gains on derivative instruments (net of tax of $0 and $(1,332), respectively)	0	1,877
Reclassifications of net losses on derivative instruments (net of tax of $(351) and $(276), respectively)	495	390
Benefit plans reclassifications of actuarial losses and prior service costs (net of tax of $(169) and $(113), respectively)	239	160
Other comprehensive income	734	2,427
Comprehensive income	$ 44,999	$ 25,778