Acquisition Activity - Schedule of Total Contractually Required Principal and Interest (Details) - USD ($) $ in Thousands	Sep. 30, 2016	May 16, 2016	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Business Acquisition [Line Items]
Accretable yield	$ (38,124)		$ (44,489)	$ (50,889)	$ (67,660)
HF Financial Corp | Receivables acquired with deteriorated credit quality
Business Acquisition [Line Items]
Contractually required principal and interest		$ 83,710
Non-accretable difference		(28,516)
Cash flows expected to be collected		55,194
Accretable yield		(3,662)
Total purchased credit impaired loans acquired		$ 51,532