Fair Value - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets
Securities available-for-sale	$ 121,000	$ 235,774
Securities held-to-maturity	539,433	304,927
Federal Home Loan Bank, Federal Reserve Bank stock and other investments, at cost	32,499	33,522
I/O strips receivables	246	305
Liabilities
Subordinated Debt.	39,878	39,740
Significant Other Observable Inputs (Level 2)
Assets
I/O strips receivables	246	305
Carrying amount
Assets
Cash and cash equivalents	1,621,347	1,131,073
Securities available-for-sale	121,000	235,774
Securities held-to-maturity	537,285	297,389
Loans (including loans held-for-sale), net	2,792,857	2,576,560
Federal Home Loan Bank, Federal Reserve Bank stock and other investments, at cost	32,499	33,522
Accrued interest receivable	9,868	10,546
I/O strips receivables	246	305
Liabilities
Time deposits	149,180	153,407
Other deposits	4,577,201	3,761,079
Subordinated Debt.	39,878	39,740
Accrued interest payable	1,062	545
Carried at fair value
Assets
Cash and cash equivalents	1,621,347	1,131,073
Securities available-for-sale	121,000	235,774
Securities held-to-maturity	539,433	304,927
Loans (including loans held-for-sale), net	2,810,897	2,574,692
Accrued interest receivable	9,868	10,546
I/O strips receivables	246	305
Liabilities
Time deposits	149,441	153,740
Other deposits	4,577,201	3,761,079
Subordinated Debt.	40,478	40,340
Accrued interest payable	1,062	545
Carried at fair value \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash and cash equivalents	1,621,347	1,131,073
Securities available-for-sale	5,004	60,448
Accrued interest receivable	26	309
Carried at fair value \| Significant Other Observable Inputs (Level 2)
Assets
Securities available-for-sale	115,996	175,326
Securities held-to-maturity	539,433	304,927
Loans (including loans held-for-sale), net	3,678	1,699
Accrued interest receivable	1,749	1,512
I/O strips receivables	246	305
Liabilities
Time deposits	149,441	153,740
Other deposits	4,577,201	3,761,079
Subordinated Debt.	40,478	40,340
Accrued interest payable	1,062	545
Carried at fair value \| Significant Unobservable Inputs (Level 3)
Assets
Loans (including loans held-for-sale), net	2,807,219	2,572,993
Accrued interest receivable	$ 8,093	$ 8,725

Fair value as of the balance sheet date of accrued interest receivable.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the fair value of deposits other than time deposits as of the balance sheet date.

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Fair value of deposits that cannot be withdrawn before a set date without penalty or for which notice of withdrawal is required.

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Fair value portion of accrued expenses.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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Amount of investments classified as other.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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