Core Deposits and Other Intangibles - Intangible Assets Amortization Expense (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Sep. 30, 2015
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 92,109	$ 84,232
Accumulated amortization	(80,377)	(77,113)
Net intangible assets	11,732	7,119
Core Deposit Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	67,018	59,679
Accumulated amortization	(59,842)	(59,073)
Net intangible assets	7,176	606
Brand Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	8,464	8,464
Accumulated amortization	(4,700)	(4,136)
Net intangible assets	3,764	4,328
Customer Relationships Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	16,089	16,089
Accumulated amortization	(15,800)	(13,904)
Net intangible assets	289	2,185
Other
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	538	0
Accumulated amortization	(35)	0
Net intangible assets	$ 503	$ 0