Loans and Loans Held for Sale - Additional Information (Details) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unearned income on loans and leases receivable	$ 5,200	$ 5,200
Net unamortized discount related to purchase accounting fair value adjustments	2,800	7,100
Loans receivable, net	$ 5,765,934	$ 5,615,212
Number of loan modified \| loan	15
Number of commitments to lend additional funds on TDRs \| loan	2
Commitment to lend additional funds on TDRs	$ 200
Number of TDRs returned back to accruing status \| loan	1	5
Financial receivable trouble debt restructuring reclassified to accruing trouble debt restructuring status	$ 2,000	$ 900
Minimum period of loan payment defaults following restructure for TDRs to be in default	90 days
Number of defaulted TDRs that were restructured within twelve months prior to defaulting \| loan	0	0
Decrease in nonperforming assets	$ 18,900
Nonperforming assets	$ 24,407	$ 43,314
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of commercial loans in total portfolio loans	78.00%	78.00%
Loans recorded investment	$ 4,503,594	$ 4,355,395
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net	$ 2,685,994	2,498,476
Number of loan modified \| loan	5
Loans modified not considered to be troubled debt restructuring	$ 7,500
Commercial real estate \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans recorded investment	2,685,994	2,498,476
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net	$ 1,433,266	1,401,035
Number of loan modified \| loan	10
Loans modified not considered to be troubled debt restructuring	$ 10,800
Number of nonperforming, impaired loans paid off during the period \| loan	2
Balance of nonperforming, impaired loans paid off during the period	$ 10,500
Commercial and industrial \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans recorded investment	1,433,266	1,401,035
Commercial construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net	384,334	455,884
Commercial construction \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans recorded investment	384,334	455,884
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net	698,774	701,982
Consumer construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net	$ 4,551	$ 5,906
CRE and Commercial Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Out-of-state exposure of combined portfolio	5.20%	5.20%
Percentage of total loans out-of-state	2.80%	2.70%
CRE and Commercial Construction \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans recorded investment	$ 3,100,000	$ 3,000,000
Combined percentage of commercial real estate and commercial construction in total commercial loans	68.00%	68.00%
Combined percentage of commercial real estate and commercial construction in total portfolio loans	53.00%	53.00%
Concentration risk percentage	0.00%	0.00%
Maximum concentration of commercial real estate and commercial construction portfolio in loans	14.00%	14.00%
Integrity Bancshares, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net	$ 387,000	$ 543,000
Integrity Bancshares, Inc. \| Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net	209,000	273,000
Integrity Bancshares, Inc. \| Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net	92,100	141,000
Integrity Bancshares, Inc. \| Commercial construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net	11,100	33,000
Integrity Bancshares, Inc. \| Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net	57,500	74,000
Integrity Bancshares, Inc. \| Home Equity, Installment and Other Consumer Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, net	$ 17,300	$ 22,000

Combined percentage of commercial real estate and commercial construction in commercial loans.

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Combined percentage of commercial real estate and commercial construction in portfolio loans.

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Commitment to lend additional funds.

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Financial receivable trouble debt restructuring reclassified to accruing trouble debt restructuring status.

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Financing Receivable, Nonaccrual Status and Impaired Paid Off During the Period, Number of Contracts

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Financing Receivable, Nonaccrual Status and Impaired Paid Off During the Period, Recorded Investment

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Increase (Decrease) in Net Nonperforming Assets

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Loans modified not considered to be troubled debt restructuring.

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Maximum concentration of commercial real estate and commercial construction portfolio in loans.

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Net Loans Out Of State, Percentage

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Net nonperforming assets.

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Number Of Loans Modified Not Considered To Be Troubled Debt Restructuring

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Number of troubled debt restructuring loans returned back to accruing status.

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Number of Commitment To Lend Additional Funds

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Number of Defaulted Troubled Debt Restructuring Loans Restructured Whiting Twelve Months Prior to Defaulting

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Out of state exposure of combined portfolio.

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Percentage of commercial loans in portfolio loans.

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Period of loans in default treated as troubled debt restructuring.

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- Definition

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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- Definition

Total remaining unamortized or unaccreted amounts of premiums, discounts, and intangible assets, in years subsequent to the year of acquisition, when the total amounts of remaining discounts, premiums, and intangible assets exceed 30 percent of stockholders' equity.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Amount of deferred interest and fee income, unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of acquired loans. Excludes amounts for loans and leases covered under loss sharing agreements.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes loans held for sale. Excludes loans and leases covered under loss sharing agreements.

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