Fair Value of Financial Instruments - Changes in AOCI (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Jun. 30, 2017	Jun. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		$ 882,915
Balance at end of period	$ 687,810	687,810
Accumulated net gain (loss) from cash flow hedges attributable to parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(1,756)	(4,206)
Change in fair value of hedging instruments	(513)	1,548
Amounts reclassified to earnings	39	428
Net current period other comprehensive income	(474)	1,976
Balance at end of period	$ (2,230)	$ (2,230)