Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Net income (loss)	$ 141,810	$ 137,684	$ 244,671	$ 235,279
Income allocated to participating securities	231	296	405	520
Income available to common shareholders	$ 141,579	$ 137,388	$ 244,266	$ 234,759
Basic and diluted net income per share	$ 1.38	$ 1.35	$ 2.38	$ 2.31
Weighted Average Number of Shares Outstanding, Basic and Diluted	102,946	101,746	102,837	101,667