Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Assets [Abstract]
Cash and due from banks	$ 150,085	$ 201,487
Interest-bearing bank deposits	282,802	41,987
Cash and cash equivalents	432,887	243,474
Securities available for sale	1,774,626	1,783,208
Loans, net of unearned discounts and deferred fees, including $0 and $31,891 of loans covered by a FDIC loss share agreement at September 30, 2020 and 2019, respectively, and $655,185 and $812,991 of loans at fair value under the fair value option at September 30, 2020 and 2019, respectively, and $12,371 and $7,351 of loans held for sale at September 30, 2020 and 2019, respectively	10,076,142	9,706,763
Allowance for loan and lease losses	(149,887)	(70,774)
Net loans	9,926,255	9,635,989
Premises and equipment, including $600 and $2,757 of property held for sale at September 30, 2020 and 2019, respectively	119,054	120,645
Accrued interest receivable	54,658	58,699
Other repossessed property, including $0 of property covered by a FDIC loss share agreement at September 30, 2020 and 2019	20,034	36,764
Goodwill	0	739,023
Cash surrender value of life insurance policies	31,658	30,796
Net deferred tax assets	47,709	7,286
Other assets	197,558	132,417
Total assets	12,604,439	12,788,301
Deposits, Interest-bearing and Noninterest-bearing, Alternative [Abstract]
Noninterest-bearing	2,586,743	1,956,025
Interest-bearing	8,422,036	8,344,314
Total deposits	11,008,779	10,300,339
Securities sold under agreements to repurchase	65,506	68,992
FHLB advances and other borrowings	195,000	340,000
Subordinated debentures and subordinated notes payable	108,832	108,636
Accrued expenses and other liabilities	63,389	70,085
Total liabilities	11,441,506	10,888,052
Stockholders’ equity
Common stock, $0.01 par value, authorized 500,000,000 shares; 55,014,189 shares issued and outstanding at September 30, 2020 and 56,283,659 shares issued and outstanding at September 30, 2019	550	563
Additional paid-in capital	1,183,647	1,228,714
Retained earnings	(57,169)	657,475
Accumulated other comprehensive income	35,905	13,497
Total stockholders' equity	1,162,933	1,900,249
Total liabilities and stockholders' equity	$ 12,604,439	$ 12,788,301