Schedule of Allowance for Loan Losses by Portfolio Segment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Certain Loans and Debt Securities Acquired in Transfer, Allowance for Credit Losses Due to Subsequent Impairment	$ 117
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	74,200	85,339
Provision charged to operating expense	1,095us-gaap_ProvisionForLoanAndLeaseLosses	(5,000)us-gaap_ProvisionForLoanAndLeaseLosses
Less loans charged-off	(1,861)	(2,791)
Add back recoveries of loans previously charged-off	1,902	3,823
Ending balance	75,336	81,371
Allowance for loan losses:
Loans individually evaluated for impairment	7,468	7,494
Loans collectively evaluated for impairment	67,868	73,877
Ending balance	75,336	81,371
Total loans:
Individually evaluated for impairment	85,033	101,929
Individually evaluated for impairment	4,842,273	4,262,909
Total loans	4,927,306	4,364,838	4,897,443
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	53,884	63,923
Provision charged to operating expense	(1,031)	(3,375)
Less loans charged-off	(186)	(1,085)
Add back recoveries of loans previously charged-off	992	367
Ending balance	53,659	59,830
Allowance for loan losses:
Loans individually evaluated for impairment	3,958	5,952
Loans collectively evaluated for impairment	49,701	53,878
Ending balance	53,659	59,830
Total loans:
Individually evaluated for impairment	62,780	86,772
Individually evaluated for impairment	3,223,969	2,788,421
Total loans	3,286,749	2,875,193
Total consumer loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	5,035	6,193
Provision charged to operating expense	1,125	(578)
Less loans charged-off	(1,301)	(846)
Add back recoveries of loans previously charged-off	640	608
Ending balance	5,499	5,377
Allowance for loan losses:
Loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	5,499	5,377
Ending balance	5,499	5,377
Total loans:
Individually evaluated for impairment	0	0
Individually evaluated for impairment	768,462	670,406
Total loans	768,462	670,406
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	14,307	14,747
Provision charged to operating expense	993	(1,072)
Less loans charged-off	(374)	(796)
Add back recoveries of loans previously charged-off	270	2,822
Ending balance	15,196	15,701
Allowance for loan losses:
Loans individually evaluated for impairment	2,905	1,458
Loans collectively evaluated for impairment	12,291	14,243
Ending balance	15,196	15,701
Total loans:
Individually evaluated for impairment	21,192	14,464
Individually evaluated for impairment	732,957	692,773
Total loans	754,149	707,237
Agriculture
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	974	476
Provision charged to operating expense	8	25
Less loans charged-off	0	(64)
Add back recoveries of loans previously charged-off	0	26
Ending balance	982	463
Allowance for loan losses:
Loans individually evaluated for impairment	605	84
Loans collectively evaluated for impairment	377	379
Ending balance	982	463
Total loans:
Individually evaluated for impairment	1,061	693
Individually evaluated for impairment	116,508	107,683
Total loans	117,569	108,376
Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0
Provision charged to operating expense	0	0
Less loans charged-off	0	0
Add back recoveries of loans previously charged-off	0	0
Ending balance	0	0
Allowance for loan losses:
Loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	0	0
Ending balance	0	0
Total loans:
Individually evaluated for impairment	0	0
Individually evaluated for impairment	377	3,626
Total loans	$ 377	$ 3,626

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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For loans and debt securities, 1) for which at acquisition it was probable that the investor would be unable to collect all contractually required payments receivable, and 2) for which it is further probable that the investor will not be able to collect all cash flows expected at acquisition (plus any additional cash flows expected due to changes in estimate after acquisition), the allowance for credit losses recorded to reflect the impairment since acquisition.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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The balance of financing receivables that were individually evaluated for impairment.

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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 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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Amount of expense related to estimated loss from loan and lease transactions.

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