Fair Value Measurements and Fair Value of Financial Instruments, Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Reclassification of net unrealized gain on cash flow hedges from AOCI to interest expense	$ 269	$ (50)
Financial assets [Abstract]
HTM securities	477,409		$ 481,871
Financial liabilities [Abstract]
Time deposits	840,425		806,766
Long-term debt	88,824		88,869
Junior subordinated debt	101,196		101,196
Carrying Amount [Member] \| Level 2 [Member]
Financial assets [Abstract]
HTM securities	487,126		484,073
Financial liabilities [Abstract]
Time deposits	840,425		806,766
Long-term debt	88,824		88,869
Junior subordinated debt	101,196		101,196
Carrying Amount [Member] \| Level 3 [Member]
Financial assets [Abstract]
Net loans	6,576,924		6,515,273
Estimated Fair Value [Member] \| Level 2 [Member]
Financial assets [Abstract]
HTM securities	477,409		481,871
Financial liabilities [Abstract]
Time deposits	833,181		801,294
Long-term debt	87,538		88,346
Junior subordinated debt	101,986		104,593
Estimated Fair Value [Member] \| Level 3 [Member]
Financial assets [Abstract]
Net loans	6,612,392		6,651,931
Not Designated as Hedging Instrument [Member] \| Interest Rate Swaps [Member] \| Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, notional amount	551,800		481,200
Fair value of derivative asset	9,200		200
Not Designated as Hedging Instrument [Member] \| Interest Rate Swaps [Member] \| Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, notional amount	551,800		481,200
Fair value of derivative liability	9,200		200
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] \| Interest Expense [Member]
Derivatives, Fair Value [Line Items]
Reclassification of net unrealized gain on cash flow hedges from AOCI to interest expense	400	$ 100
Amount expected to be reclassified as a reduction to interest expense for CF hedges	2,600
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	$ 4,200		$ 3,500

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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Amount after tax of estimated reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) expected to be realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss) within next 12 months.

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Nominal or face amount used to calculate payments on the derivative asset.

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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, before 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 elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Nominal or face amount used to calculate payments on the derivative liability.

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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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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 after tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Amount of time deposit liabilities, including certificates of deposit.

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