Core Deposits and Other Intangibles - Intangible Assets Amortization Expense (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 92,109	$ 92,109
Accumulated amortization	(81,216)	(80,377)
Total	10,893	11,732
Core Deposit Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	67,018	67,018
Accumulated amortization	(60,229)	(59,842)
Total	6,789	7,176
Brand Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	8,464	8,464
Accumulated amortization	(4,841)	(4,700)
Total	3,623	3,764
Customer Relationships Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	16,089	16,089
Accumulated amortization	(16,089)	(15,800)
Total	0	289
Other Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	538	538
Accumulated amortization	(57)	(35)
Total	$ 481	$ 503