Accumulated Other Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss)
AOCI, net of tax - beginning balance	$ (13,686)	$ (8,181)
Net gains on IRPAs	1,877
Reclassifications, net of tax	160	131
AOCI, net of tax - ending balance	(11,259)	(7,659)
Interest Rate Protection Agreements
Accumulated Other Comprehensive Income (Loss)
Reclassifications, net of tax	390	391
Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss)
AOCI, net of tax - beginning balance	(9,276)	(6,311)
Net gains on IRPAs	0
Reclassifications, net of tax	160	131
AOCI, net of tax - ending balance	(9,116)	(6,180)
Postretirement Benefit Plans | Interest Rate Protection Agreements
Accumulated Other Comprehensive Income (Loss)
Reclassifications, net of tax	0	0
Derivative Instruments
Accumulated Other Comprehensive Income (Loss)
AOCI, net of tax - beginning balance	(4,410)	(1,870)
Net gains on IRPAs	1,877
Reclassifications, net of tax	0	0
AOCI, net of tax - ending balance	(2,143)	(1,479)
Derivative Instruments | Interest Rate Protection Agreements
Accumulated Other Comprehensive Income (Loss)
Reclassifications, net of tax	$ 390	$ 391