Acquisition Activity - Schedule of Consideration (Details) - USD ($) shares in Thousands, $ in Thousands	May 16, 2016	Dec. 31, 2016	Sep. 30, 2016
Non-equity consideration:
Goodwill		$ 739,023	$ 739,023
HF Financial Corporation
Equity consideration:
Common stock issued (in shares)	3,448,119
Common stock issued	$ 107,478
Non-equity consideration:
Cash	34,487
Total consideration paid	141,965
Fair value of net assets acquired including identifiable intangible assets	100,749
Goodwill	$ 41,216