Disclosures About Fair Value of Financial Instruments - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Carrying Amount	$ 251,726	$ 146,323	$ 413,242	$ 264,709
Cash and cash equivalents, Estimated Fair Value	251,726	146,323
Debt securities, available for sale	1,157,944
Debt securities, available for sale, Estimated Fair Value	1,157,944
Investment securities, at fair value	1,161,000	471,371
Investments securities, available for sale, fair value		471,371
Equity securities, carrying amount	3,056
Equity securities, Estimated Fair Value	3,056
Loans held for sale, Carrying Amount	1,931,781	1,939,485
Loans held for sale, Estimated Fair Value	1,931,781	1,939,659
Loans receivable, net of allowance for loan losses, Carrying Amount	7,143,438	6,730,243
Loans receivable, net of allowance for loan losses, Estimated Fair Value	7,127,315	6,676,763
FHLB, Federal Reserve Bank and other restricted stock, Carrying Amount	136,066	105,918
FHLB, Federal Reserve Bank and other restricted stock, Estimated Fair Value	136,066	105,918
Derivative assets	16,247	9,752
Deposits, Carrying Amount	7,295,954	6,800,142
Deposits, Estimated Fair Value	7,288,828	6,796,095
Federal funds purchased, Carrying Amount	105,000	155,000
Federal funds purchased, Estimated Fair Value	105,000	155,000
FHLB advances, Carrying Amount	2,389,797	1,611,860
FHLB advances, Estimated Fair Value	2,389,785	1,611,603
Other borrowings, Carrying Amount	186,888	186,497
Other borrowings, Estimated Fair Value	185,364	193,557
Subordinated debt, Carrying Amount	108,929	108,880
Subordinated debt, Estimated Fair Value	114,675	115,775
Derivative liabilities	13,698	10,074
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Estimated Fair Value	251,726	146,323
Debt securities, available for sale, Estimated Fair Value	0
Investments securities, available for sale, fair value		3,352
Equity securities, Estimated Fair Value	3,056
Loans held for sale, Estimated Fair Value	0	0
Loans receivable, net of allowance for loan losses, Estimated Fair Value	0	0
FHLB, Federal Reserve Bank and other restricted stock, Estimated Fair Value	0	0
Derivative assets	0	0
Deposits, Estimated Fair Value	5,223,793	4,894,449
Federal funds purchased, Estimated Fair Value	105,000	155,000
FHLB advances, Estimated Fair Value	1,504,797	881,860
Other borrowings, Estimated Fair Value	63,554	65,072
Subordinated debt, Estimated Fair Value	0	0
Derivative liabilities	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Estimated Fair Value	0	0
Debt securities, available for sale, Estimated Fair Value	1,157,944
Investments securities, available for sale, fair value		468,019
Equity securities, Estimated Fair Value	0
Loans held for sale, Estimated Fair Value	1,931,781	1,795,294
Loans receivable, net of allowance for loan losses, Estimated Fair Value	0	0
FHLB, Federal Reserve Bank and other restricted stock, Estimated Fair Value	136,066	105,918
Derivative assets	16,114	9,692
Deposits, Estimated Fair Value	2,065,035	1,901,646
Federal funds purchased, Estimated Fair Value	0	0
FHLB advances, Estimated Fair Value	884,988	729,743
Other borrowings, Estimated Fair Value	121,810	128,485
Subordinated debt, Estimated Fair Value	114,675	115,775
Derivative liabilities	13,698	10,074
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Estimated Fair Value	0	0
Debt securities, available for sale, Estimated Fair Value	0
Investments securities, available for sale, fair value		0
Equity securities, Estimated Fair Value	0
Loans held for sale, Estimated Fair Value	0	144,365
Loans receivable, net of allowance for loan losses, Estimated Fair Value	7,127,315	6,676,763
FHLB, Federal Reserve Bank and other restricted stock, Estimated Fair Value	0	0
Derivative assets	133	60
Deposits, Estimated Fair Value	0	0
Federal funds purchased, Estimated Fair Value	0	0
FHLB advances, Estimated Fair Value	0	0
Other borrowings, Estimated Fair Value	0	0
Subordinated debt, Estimated Fair Value	0	0
Derivative liabilities	$ 0	$ 0

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Equity Securities

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Equity Securities, at Fair Value

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Federal Home Loan Bank Stock And Federal Reserve Bank Stock Fair Value

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Subordinated Debt Fair Value Disclosure

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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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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Amount 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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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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The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of short term borrowing where a bank borrows, at the federal funds rate, from another bank.

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Fair value portion of short term borrowing where a bank borrows, at the federal funds rate, from another bank.

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Amount of advances from the Federal Home Loan Bank (FHLB).

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Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

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Amount of Federal Home Loan Bank (FHLB) and Federal Reserve Bank stock.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums over and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes loans and leases covered under loss sharing agreements.

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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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, after allowance for bad debt, of loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

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The carrying amount as of the balance sheet date for the aggregate of other miscellaneous borrowings owed by the reporting entity.

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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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