Fair Value of Financial Instruments - Changes in AOCI (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period		$ 649,731
Balance at end of period	$ 672,092	672,092
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	(763)	(2,133)
Change in fair value of hedging instruments	1,157	1,970
Amounts reclassified to earnings	304	861
Net current period other comprehensive income	1,461	2,831
Balance at end of period	$ 698	$ 698