Loans and Allowance for Loan Losses - Textual (Details)	3 Months Ended
Mar. 31, 2019 USD ($) loan	Mar. 31, 2018 USD ($) loan	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 11,740,000,000		$ 11,720,000,000
Recorded investment	57,579,000		39,770,000
Impaired loan, related allowance	521,000		684,000
Interest income recognized	375,000	$ 350,000
Average Investment in Impaired Loans	$ 48,675,000	$ 45,596,000
Troubled debt, number of contracts \| loan	0	2
Balance prior to TDR		$ 152,000
Financial impact on date of restructure	$ 0
Foreclosed assets and other real estate owned	18,952,000		25,565,000
Risk Rate 6 \| Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired	3,700,000		4,100,000
Risk Ratings 6,7, and 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired excluding loans accounted for under ASC Topic 310-30	177,400,000		119,000,000
Risk Ratings 6,7, and 8 \| Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired excluding loans accounted for under ASC Topic 310-30	77,200,000		50,400,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in process of foreclosure, amount	3,498,000		3,899,000
OREO Received in Full or Partial Satisfaction of Loans \| Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Foreclosed assets and other real estate owned	4,716,000		3,530,000
Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,162,678,000		5,966,453,000
Recorded investment	24,976,000		24,253,000
Impaired loan, related allowance	412,000		$ 247,000
Interest income recognized	176,000	236,000
Average Investment in Impaired Loans	24,615,000	$ 31,892,000
Troubled debt, number of contracts \| loan		1
Balance prior to TDR		$ 61,000
Financial impact on date of restructure		0
Real estate \| OREO Received in Full or Partial Satisfaction of Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance prior to TDR	$ 0	$ 294,300
Commercial Real Estate \| Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans with subsequent default \| loan	1	1
Write-down of impaired loans	$ 138,000	$ 66,300
Transfers of loans		$ 294,300

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The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and other-than-temporary impairments), for loans accounted for as debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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Number of financing receivables that have been modified by troubled debt restructurings.

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Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

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Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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Amount of allowance for credit losses related to recorded investment.

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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.

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Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

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Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

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Value transferred from mortgage loans to real estate owned (REO) in noncash transactions.

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