Fair Value - Estimated fair value and related carrying amount, of the Company's financial instruments (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Financial assets:
Loans held for sale	$ 47,796	$ 36,968	$ 22,925
Financial liabilities:
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	298,029	331,969	270,649
Increase (Decrease) in Loans Held-for-sale	214,785	207,909
Other borrowings	816,414	115,754	266,084
Carrying Amount
Financial assets:
Cash and cash equivalents	851,971	396,849	408,983
Investment securities	1,766,400	1,597,727	1,542,671
Loans held for sale	47,796	36,968	22,925
Loans, net of allowance for loan losses (1)	11,167,979	10,778,068	10,962,037
Accrued interest receivable	38,650	33,751	35,997
Mortgage servicing rights	30,332	35,107	34,727
Interest rate swap - non-designated hedge	14,561	7,750	3,824
Other derivative financial instruments (mortgage banking related)	3,026	1,098	1,267
Financial liabilities:
Deposits	11,922,280	11,638,289	11,646,933
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	298,029	331,969	270,649
Other borrowings	816,414	115,754	266,084
Accrued interest payable	6,168	3,882	4,719
Interest rate swap - non-designated hedge	15,952	7,981	4,373
Interest rate swap - cash flow hedge	14,334	116	48
Fair Value
Financial assets:
Cash and cash equivalents	851,971	396,849	408,983
Investment securities	1,766,400	1,597,731	1,542,671
Loans held for sale	47,796	36,968	22,925
Loans, net of allowance for loan losses (1)	11,278,624	10,547,778	10,613,571
Accrued interest receivable	38,650	33,751	35,997
Mortgage servicing rights	30,332	35,107	34,727
Interest rate swap - non-designated hedge	14,561	7,750	3,824
Other derivative financial instruments (mortgage banking related)	3,026	1,098	1,267
Financial liabilities:
Deposits	11,124,796	10,675,705	10,561,394
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	298,029	331,969	270,649
Other borrowings	819,306	119,221	269,134
Accrued interest payable	6,168	3,882	4,719
Interest rate swap - non-designated hedge	15,952	7,981	4,373
Interest rate swap - cash flow hedge	14,334	116	48
Commitments to extend credit \| Fair Value
Financial liabilities:
Commitments to extend credit	27,579	(62,060)	(88,424)
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	851,971	396,849	408,983
Investment securities	49,124	19,229	25,604
Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities	1,717,276	1,578,502	1,517,067
Loans held for sale	47,796	36,968	22,925
Accrued interest receivable	7,880	7,333	6,908
Interest rate swap - non-designated hedge	14,561	7,750	3,824
Other derivative financial instruments (mortgage banking related)	3,026	1,098	1,267
Financial liabilities:
Deposits	11,124,796	10,675,705	10,561,394
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	298,029	331,969	270,649
Other borrowings	819,306	119,221	269,134
Accrued interest payable	6,168	3,882	4,719
Interest rate swap - non-designated hedge	15,952	7,981	4,373
Interest rate swap - cash flow hedge	14,334	116	48
Significant Other Observable Inputs (Level 2) \| Commitments to extend credit
Financial liabilities:
Commitments to extend credit	27,579	(62,060)	(88,424)
Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, net of allowance for loan losses (1)	11,278,624	10,547,778	10,613,571
Accrued interest receivable	30,770	26,418	29,089
Mortgage servicing rights	$ 30,332	$ 35,107	$ 34,727

Fair value of accrued interest payable as on date.

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Fair value of accrued interest receivable as on date.

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Fair value portion of arrangements to extend credit.

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The 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, the 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. The item represents residential mortgage servicing rights as presented on the statement of financial position which are due to the entity as of the balance sheet date.

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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 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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Amount after offset of short term borrowing where a bank borrows, at the federal funds rate, from another bank and securities that an entity sells and agrees to repurchase at a specified date for a specified price.

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The increase (decrease) during the reporting period in the value of loans or securitized loans that are held with the intention to sell in the near future.

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Fair value as of the balance sheet date of all interest rate derivative liabilities designated as cash flow hedging instruments.

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Fair value as of the balance sheet date of all derivative assets not designated as hedging instruments.

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Fair value as of the balance sheet date of all derivative liabilities not designated as hedging instruments.

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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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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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