Core Deposits and Other Intangibles - Intangible Assets Amortization Expense (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 92,109	$ 92,109
Accumulated amortization	(82,304)	(80,377)
Total	9,805	11,732
Core Deposit Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	67,018	67,018
Accumulated amortization	(60,989)	(59,842)
Total	6,029	7,176
Brand Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	8,464	8,464
Accumulated amortization	(5,123)	(4,700)
Total	3,341	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	(103)	(35)
Total	$ 435	$ 503