Fair Value Measurements and Fair Value of Financial Instruments, Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financial assets [Abstract]
Securities held to maturity	$ 513,654	$ 525,050
Financial liabilities [Abstract]
Time deposits	826,080	872,411
Long-term debt	104,023	104,087
Junior subordinated debt	101,196	101,196
Carrying Amount [Member] \| Level 2 [Member]
Financial assets [Abstract]
Securities held to maturity	515,793	527,948
Financial liabilities [Abstract]
Time deposits	826,080	872,411
Long-term debt	104,023	104,087
Junior subordinated debt	101,196	101,196
Carrying Amount [Member] \| Level 3 [Member]
Financial assets [Abstract]
Net loans	6,206,603	6,132,857
Estimated Fair Value [Member] \| Level 2 [Member]
Financial assets [Abstract]
Securities held to maturity	513,654	525,050
Financial liabilities [Abstract]
Time deposits	821,557	868,153
Long-term debt	103,976	104,113
Junior subordinated debt	101,922	102,262
Estimated Fair Value [Member] \| Level 3 [Member]
Financial assets [Abstract]
Net loans	6,354,631	6,273,233
Not Designated as Hedging Instrument [Member] \| Interest Rate Swaps [Member] \| Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, notional amount	394,900	371,100
Fair value of derivative asset	700	300
Not Designated as Hedging Instrument [Member] \| Interest Rate Swaps [Member] \| Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, notional amount	394,900	371,100
Fair value of derivative liability	700	300
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional amount	250,000	250,000
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swaps [Member] \| Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	$ 3,200	$ 2,700

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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Fair value, before 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 elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value of investments in debt securities classified as held-to-maturity.

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Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

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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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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of time deposit liabilities, including certificates of deposit.

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