Acquisition Activity - Schedule of Total Contractually Required Principal and Interest (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	May 16, 2016	Mar. 31, 2016	Sep. 30, 2015
Business Acquisition [Line Items]
Accretable yield	$ (48,134)	$ (38,705)	$ (38,124)	$ (40,976)		$ (39,843)	$ (44,489)
HF Financial Corporation | Acquired receivables subject to ASC 310-30
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