Loans (Loans receivable) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Dec. 31, 2016
Loans and Leases [Line Items]
Gross loans receivable held to maturity	$ 5,363,737	$ 5,353,702
Unearned discount	(668)	(699)
Deferred loan fees	(1,465)	(1,284)
Total net loans receivable held to maturity	5,361,604	5,351,719
Allowance for loan losses	(54,999)	(54,324)
Loans receivable, net	5,306,605	5,297,395
Loans secured by residential real estate property in process of foreclosure	$ 2,600
Threshold period past due, nonperforming status of loans and leases	90 days
Commercial
Loans and Leases [Line Items]
Gross loans receivable held to maturity	$ 3,849,748	3,825,847
Commercial \| Minimum
Loans and Leases [Line Items]
Length of loan agreements	1 year
Commercial \| Maximum
Loans and Leases [Line Items]
Length of loan agreements	5 years
Commercial \| Commercial
Loans and Leases [Line Items]
Gross loans receivable held to maturity	$ 1,314,393	1,287,265
Commercial \| Commercial real estate
Loans and Leases [Line Items]
Gross loans receivable held to maturity	2,535,355	2,538,582
Agricultural and agricultural real estate
Loans and Leases [Line Items]
Gross loans receivable held to maturity	481,125	489,318
Residential real estate
Loans and Leases [Line Items]
Gross loans receivable held to maturity	$ 604,902	617,924
Residential real estate \| Minimum
Loans and Leases [Line Items]
Length of loan agreements	10 years
Residential real estate \| Maximum
Loans and Leases [Line Items]
Length of loan agreements	30 years
Consumer
Loans and Leases [Line Items]
Gross loans receivable held to maturity	$ 427,962	$ 420,613
Consumer \| Citizens Finance Co \| Loans and Finance Receivables
Loans and Leases [Line Items]
Concentration risk, percentage	18.00%

Loans and Leases [Line Items]

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Loans and Leases Receivable, Contract Term

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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.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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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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Amount before allowance and after 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. Excludes loans and leases covered under loss sharing agreements.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums over and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes 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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Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale.

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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

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