Earnings Per Share (Reconciliation of Net Earnings to Net Earnings Per Share Basic and Diluted) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share
Net earnings	$ 62,228	$ 53,626	$ 38,105	$ 46,548	$ 63,147	$ 51,047	$ 40,824	$ 25,820	$ 200,507	$ 180,838	$ 181,452
Basic shares outstanding									61,366	61,893	64,684
Dilutive effect of stock options and restricted stock									2,146	1,663	1,372
Diluted shares outstanding									63,512	63,556	66,056
Basic earnings per share	$ 1.02	$ 0.87	$ 0.62	$ 0.76	$ 1.03	$ 0.83	$ 0.66	$ 0.41	$ 3.27	$ 2.92	$ 2.81
Diluted earnings per share	$ 0.98	$ 0.85	$ 0.60	$ 0.73	$ 0.99	$ 0.81	$ 0.65	$ 0.40	$ 3.16	$ 2.85	$ 2.75