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, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share
Net earnings	$ 74,512	$ 49,117	$ 38,489	$ 18,260	$ 62,228	$ 53,626	$ 38,105	$ 46,548	$ 180,378	$ 200,507	$ 180,838
Basic shares outstanding									61,493	61,366	61,893
Dilutive effect of stock options and restricted stock									2,383	2,146	1,663
Diluted shares outstanding									63,876	63,512	63,556
Basic earnings per share	$ 1.21	$ 0.80	$ 0.63	$ 0.30	$ 1.02	$ 0.87	$ 0.62	$ 0.76	$ 2.93	$ 3.27	$ 2.92
Diluted earnings per share	$ 1.16	$ 0.77	$ 0.60	$ 0.29	$ 0.98	$ 0.85	$ 0.60	$ 0.73	$ 2.82	$ 3.16	$ 2.85