Consolidated Statements of Cash Flows (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities:
Net income	$ 153,151,000us-gaap_NetIncomeLoss	$ 126,351,000us-gaap_NetIncomeLoss	$ 107,835,000us-gaap_NetIncomeLoss
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for probable loan losses	14,423,000us-gaap_ProvisionForLoanAndLeaseLosses	22,968,000us-gaap_ProvisionForLoanAndLeaseLosses	27,959,000us-gaap_ProvisionForLoanAndLeaseLosses
Specific reserve, other real estate owned	779,000	1,204,000	1,776,000
Depreciation of bank premises and equipment	24,013,000us-gaap_DepreciationNonproduction	26,017,000us-gaap_DepreciationNonproduction	26,756,000us-gaap_DepreciationNonproduction
Gain on sale of bank premises and equipment	(3,658,000)	(2,089,000)	(538,000)
(Gain) loss on sale of other real estate owned	(933,000)	(460,000)	488,000
Accretion of investment securities discounts	(2,608,000)iboc_AccretionOfDiscountsInvestments	(4,025,000)iboc_AccretionOfDiscountsInvestments	(3,195,000)iboc_AccretionOfDiscountsInvestments
Amortization of investment securities premiums	26,729,000	44,245,000	30,501,000
Investment securities transactions, net	(1,283,000)us-gaap_GainLossOnSaleOfSecuritiesNet	(9,601,000)us-gaap_GainLossOnSaleOfSecuritiesNet	(38,446,000)us-gaap_GainLossOnSaleOfSecuritiesNet
Impairment charges on available for sale securities	817,000	1,374,000	1,039,000
Amortization of identified intangible assets	2,389,000us-gaap_AmortizationOfIntangibleAssets	4,633,000us-gaap_AmortizationOfIntangibleAssets	4,651,000us-gaap_AmortizationOfIntangibleAssets
Stock based compensation expense	1,058,000us-gaap_ShareBasedCompensation	414,000us-gaap_ShareBasedCompensation	474,000us-gaap_ShareBasedCompensation
Earnings from affiliates and other investments	(10,903,000)	(18,806,000)	(9,892,000)
Deferred tax (benefit) expense	(1,027,000)us-gaap_DeferredIncomeTaxExpenseBenefit	(1,817,000)us-gaap_DeferredIncomeTaxExpenseBenefit	7,923,000us-gaap_DeferredIncomeTaxExpenseBenefit
(Increase) decrease in accrued interest receivable	(807,000)	380,000	968,000
(Increase) decrease in other assets	(1,621,000)	20,612,000	(5,392,000)
Increase (decrease) in other liabilities	(7,482,000)	(2,274,000)	7,106,000
Net cash provided by operating activities	193,037,000	209,126,000	160,013,000
Investing activities:
Proceeds from maturities of securities		1,200,000	1,125,000
Proceeds from sales and calls of available for sale securities	621,588,000	178,123,000	1,382,231,000
Purchases of available for sale securities	(971,358,000)	(1,384,254,000)	(3,081,034,000)
Principal collected on mortgage backed securities	787,361,000	1,223,532,000	1,294,197,000
Net (increase) decrease in loans	(502,129,000)	(444,919,000)	170,072,000
Purchases of other investments	(20,602,000)	(2,475,000)	(4,228,000)
Distributions from (contributions) to other investments	18,152,000iboc_DistributionsFromOtherInvestments	5,457,000iboc_DistributionsFromOtherInvestments	(7,410,000)iboc_DistributionsFromOtherInvestments
Purchases of bank premises and equipment	(50,360,000)	(50,016,000)	(62,030,000)
Proceeds from sales of bank premises and equipment	8,424,000	2,533,000	7,575,000
Proceeds from sales of other real estate owned	18,525,000	23,170,000	38,766,000
Purchase of identified intangible asset			(280,000)
Net cash used in investing activities	(90,399,000)	(447,649,000)	(261,016,000)
Financing activities:
Net increase in non-interest bearing demand deposits	263,743,000	200,760,000	538,732,000
Net increase in savings and interest bearing demand deposits	100,068,000	58,461,000	159,458,000
Net decrease in time deposits	(168,611,000)us-gaap_IncreaseDecreaseInTimeDeposits	(303,009,000)us-gaap_IncreaseDecreaseInTimeDeposits	(357,069,000)us-gaap_IncreaseDecreaseInTimeDeposits
Net decrease in securities sold under repurchase agreements	(99,031,000)	(172,298,000)	(218,950,000)
Other borrowed funds, net	(150,006,000)	474,923,000	254,866,000
Repayment of long-term debt	(15,310,000)us-gaap_RepaymentsOfLongTermDebt
Purchase of treasury stock	(18,923,000)		(1,716,000)
Redemption of Series A preferred shares			(216,000,000)
Proceeds from stock transactions	555,000	265,000	51,000
Payments of cash dividends - common	(34,762,000)us-gaap_PaymentsOfDividendsCommonStock	(28,894,000)us-gaap_PaymentsOfDividendsCommonStock	(26,894,000)us-gaap_PaymentsOfDividendsCommonStock
Payments of cash dividends - preferred			(10,260,000)
Net cash (used in) provided by financing activities	(122,277,000)	230,208,000	122,218,000
(Decrease) increase in cash and cash equivalents	(19,639,000)	(8,315,000)	21,215,000
Cash and cash equivalents at beginning of year	274,785,000	283,100,000	261,885,000
Cash and cash equivalents at end of year	255,146,000	274,785,000	283,100,000
Supplemental cash flow information:
Interest paid	47,273,000us-gaap_InterestPaid	56,818,000us-gaap_InterestPaid	77,431,000us-gaap_InterestPaid
Income taxes paid	80,374,000us-gaap_IncomeTaxesPaid	60,532,000us-gaap_IncomeTaxesPaid	36,303,000us-gaap_IncomeTaxesPaid
Non-cash investing and financing activities:
Net transfers from loans to other real estate owned	$ 2,363,000us-gaap_TransferOfOtherRealEstate	$ 9,688,000us-gaap_TransferOfOtherRealEstate	$ 54,441,000us-gaap_TransferOfOtherRealEstate

The periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings when the security was purchased at a discount. As a noncash item, this element is an adjustment to net income when calculating cash provided by (used in) operations using the indirect method.

No definition available.