Earnings per Share - Schedule of EPS, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income	$ 121,253	$ 109,065	$ 104,952
Weighted average common shares outstanding	56,563,438	57,455,693	57,886,114
Dilutive effect of stock based compensation (in shares)	165,912	45,185	0
Weighted average common shares outstanding for diluted earnings per share calculation	56,729,350	57,500,878	57,886,114
Basic earnings per share (in dollars per share)	$ 2.14	$ 1.90	$ 1.81
Diluted earnings per share (in dollars per share)	$ 2.14	$ 1.90	$ 1.81
Performance stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from computation of earnings per share (in shares)	36,696	30,909
Stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from computation of earnings per share (in shares)	54,207	58,463