Loans (Loans receivable) (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Loans and Leases [Line Items]
Gross loans receivable held to maturity	$ 7,479,441	$ 6,393,226
Unearned discount	(1,420)	(556)
Deferred loan fees	(324)	(1,206)
Total net loans receivable held to maturity	7,477,697	6,391,464
Allowance for loan and lease losses	(61,324)	(55,686)
Loans receivable, net	7,416,373	6,335,778
Commercial
Loans and Leases [Line Items]
Gross loans receivable held to maturity	5,721,138	4,809,875
Commercial \| Commercial
Loans and Leases [Line Items]
Gross loans receivable held to maturity	2,034,240	1,646,606
Commercial \| Commercial real estate
Loans and Leases [Line Items]
Gross loans receivable held to maturity	3,686,898	3,163,269
Agricultural and agricultural real estate
Loans and Leases [Line Items]
Gross loans receivable held to maturity	562,353	511,588
Residential real estate
Loans and Leases [Line Items]
Gross loans receivable held to maturity	683,051	624,279
Consumer
Loans and Leases [Line Items]
Gross loans receivable held to maturity	$ 512,899	$ 447,484
Consumer \| Loans and Finance Receivables \| Citizens Finance Co
Loans and Leases [Line Items]
Concentration risk, percentage	14.00%

Loans and Leases [Line Items]

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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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No definition available.

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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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