Condensed Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 122,437	$ 122,669	$ 161,518	$ 168,887
Derivative financial instruments:
Unrealized holding gains/(losses)	(4,649)	1,892	(4,818)	2,957
Gains/(losses) reclassified to net income	2,043	(227)	2,738	(267)
Total other comprehensive income (loss)	(2,606)	1,665	(2,080)	2,690
Comprehensive income	$ 119,831	$ 124,334	$ 159,438	$ 171,577