Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Certain Financial Instruments (Details) - USD ($) $ in Thousands		Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		$ 205,446	$ 112,548
Interest-earning deposits in financial institutions		1,865,235	3,944,686
Securities available-for-sale, Carrying Amount		9,975,109
Investment in FHLB stock, Carrying Amount		17,250	17,250
Investment in FHLB stock, Fair Value		17,250	17,250
Loans and leases, net	[1]	24,154,674	22,740,984
Loans and leases held for investment, net		23,922,460
Warrants and Rights Outstanding			3,555
Other derivative assets, Carrying Amount		4,556	2,509	$ 3,771
Equity Securities, FV-NI		8,814	28,578
Servicing rights		1,002	1,228
Demand, interest checking, money market, and savings deposits		31,676,404	32,734,949
Interest-bearing Domestic Deposit, Brokered		322,732	889,976
Time deposits		1,225,759	1,372,832
Time deposits		1,216,711	1,371,527
Borrowings		991,000	0
Borrowings		991,000	0
Subordinated debentures		863,880	863,283
Subordinated Debt Obligations, Fair Value Disclosure		883,960	917,342
Derivative Liability		2,500	931
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		205,446	112,548
Interest-earning deposits in financial institutions		1,865,235	3,944,686
Investment in FHLB stock, Fair Value		0	0
Demand, interest checking, money market, and savings deposits		0	0
Interest-bearing Domestic Deposit, Brokered		0	0
Time deposits		0	0
Borrowings		991,000	0
Subordinated Debt Obligations, Fair Value Disclosure		0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		0	0
Interest-earning deposits in financial institutions		0	0
Investment in FHLB stock, Fair Value		17,250	17,250
Demand, interest checking, money market, and savings deposits		31,676,404	32,734,949
Interest-bearing Domestic Deposit, Brokered		322,732	889,976
Time deposits		1,216,711	1,371,527
Borrowings		0	0
Subordinated Debt Obligations, Fair Value Disclosure		883,960	917,342
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		0	0
Interest-earning deposits in financial institutions		0	0
Investment in FHLB stock, Fair Value		0	0
Loans and leases held for investment, net		23,922,460
Equity warrants			3,555
Demand, interest checking, money market, and savings deposits		0	0
Interest-bearing Domestic Deposit, Brokered		0	0
Time deposits		0	0
Borrowings		0	0
Subordinated Debt Obligations, Fair Value Disclosure		0	0
Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity warrants		3,771	3,555
Other derivative assets, Fair Value		4,556	2,509
Derivative liabilities		2,500	931
Fair Value, Measurements, Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity warrants		0	0
Other derivative assets, Fair Value		0	0
Equity Securities, FV-NI		8,814	28,578
Servicing rights		0	0
Derivative liabilities		0	0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity warrants		0	0
Other derivative assets, Fair Value		4,556	2,509
Equity Securities, FV-NI		0	0
Servicing rights		0	0
Derivative liabilities		2,500	931
Fair Value, Measurements, Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity warrants		3,771	3,555
Other derivative assets, Fair Value		0	0
Equity Securities, FV-NI		0	0
Servicing rights		1,002	1,228
Derivative liabilities		0	0
NonPCI and PCI Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net			23,461,156
NonPCI and PCI Loans | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net		0	0
NonPCI and PCI Loans | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net		$ 0	2,915
NonPCI and PCI Loans | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net			$ 23,458,241

[1] Excludes accrued interest receivable of $82.7 million and $80.3 million at March 31, 2022 and December 31, 2021, respectively, which is recorded in "Other assets" on the condensed consolidated balance sheets.