Consolidated Statements of Income (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest income:
Loans, including fees	$ 281,546	$ 263,027	$ 268,588
Investment securities:
Taxable	100,095us-gaap_InterestIncomeSecuritiesTaxable	87,198us-gaap_InterestIncomeSecuritiesTaxable	94,885us-gaap_InterestIncomeSecuritiesTaxable
Tax-exempt	11,767	12,877	11,663
Other interest income	191us-gaap_OtherInterestAndDividendIncome	115us-gaap_OtherInterestAndDividendIncome	503us-gaap_OtherInterestAndDividendIncome
Total interest income	393,599	363,217	375,639
Interest expense:
Savings and interest bearing demand deposits	3,597	3,762	5,288
Time deposits	12,033us-gaap_InterestExpenseTimeDeposits	15,444us-gaap_InterestExpenseTimeDeposits	23,973us-gaap_InterestExpenseTimeDeposits
Securities sold under repurchase agreements	24,616	29,171	37,645
Other borrowings	2,033iboc_InterestExpenseOtherBorrowings	1,590iboc_InterestExpenseOtherBorrowings	998iboc_InterestExpenseOtherBorrowings
Junior subordinated deferrable interest debentures	4,264	4,665	6,595
Total interest expense	46,543us-gaap_InterestExpense	54,632us-gaap_InterestExpense	74,499us-gaap_InterestExpense
Net interest income	347,056us-gaap_InterestIncomeExpenseNet	308,585us-gaap_InterestIncomeExpenseNet	301,140us-gaap_InterestIncomeExpenseNet
Provision for probable loan losses	14,423us-gaap_ProvisionForLoanAndLeaseLosses	22,968us-gaap_ProvisionForLoanAndLeaseLosses	27,959us-gaap_ProvisionForLoanAndLeaseLosses
Net interest income after provision for probable loan losses	332,633	285,617	273,181
Non-interest income:
Service charges on deposit accounts	88,586	97,087	93,128
Other service charges, commissions and fees
Banking	44,435	41,075	38,523
Non-banking	7,463us-gaap_FeesAndCommissionsOther	7,116us-gaap_FeesAndCommissionsOther	6,998us-gaap_FeesAndCommissionsOther
Investment securities transactions, net	1,283us-gaap_GainLossOnSaleOfSecuritiesNet	9,601us-gaap_GainLossOnSaleOfSecuritiesNet	38,446us-gaap_GainLossOnSaleOfSecuritiesNet
Other investments, net	22,023us-gaap_NoninterestIncomeOther	22,383us-gaap_NoninterestIncomeOther	13,339us-gaap_NoninterestIncomeOther
Other income	14,558	12,343	10,157
Total non-interest income	178,348us-gaap_NoninterestIncome	189,605us-gaap_NoninterestIncome	200,591us-gaap_NoninterestIncome
Non-interest expense:
Employee compensation and benefits	121,511us-gaap_LaborAndRelatedExpense	119,845us-gaap_LaborAndRelatedExpense	118,041us-gaap_LaborAndRelatedExpense
Occupancy	32,530us-gaap_OccupancyNet	31,766us-gaap_OccupancyNet	34,608us-gaap_OccupancyNet
Depreciation of bank premises and equipment	24,013us-gaap_DepreciationNonproduction	26,017us-gaap_DepreciationNonproduction	26,756us-gaap_DepreciationNonproduction
Professional fees	10,925us-gaap_ProfessionalFees	13,146us-gaap_ProfessionalFees	14,369us-gaap_ProfessionalFees
Deposit insurance assessments	6,082	6,737	7,709
Net expense, other real estate owned	2,358	6,896	8,929
Amortization of identified intangible assets	2,389us-gaap_AmortizationOfIntangibleAssets	4,633us-gaap_AmortizationOfIntangibleAssets	4,651us-gaap_AmortizationOfIntangibleAssets
Advertising	7,742us-gaap_AdvertisingExpense	7,034us-gaap_AdvertisingExpense	7,017us-gaap_AdvertisingExpense
Early termination fee - securities sold under repurchase agreements	11,000	12,303	31,550
Impairment charges (Total other-than-temporary impairment charges, $(366) less loss of $1,183, $(431) less loss of $1,805, and $(916) less gain of $(123), included in other comprehensive loss)	817	1,374	1,039
Other	61,676us-gaap_OtherNoninterestExpense	62,881us-gaap_OtherNoninterestExpense	60,703us-gaap_OtherNoninterestExpense
Total non-interest expense	281,043us-gaap_NoninterestExpense	292,632us-gaap_NoninterestExpense	315,372us-gaap_NoninterestExpense
Income before income taxes	229,938	182,590	158,400
Provision for income taxes	76,787us-gaap_IncomeTaxExpenseBenefit	56,239us-gaap_IncomeTaxExpenseBenefit	50,565us-gaap_IncomeTaxExpenseBenefit
Net income	153,151us-gaap_NetIncomeLoss	126,351us-gaap_NetIncomeLoss	107,835us-gaap_NetIncomeLoss
Preferred stock dividends and discount accretion			14,362
Net income available to common shareholders	$ 153,151	$ 126,351	$ 93,473
Basic earnings per common share:
Weighted average number of shares outstanding: (in shares)	66,872,500	67,195,180	67,236,681
Net income (in dollars per share)	$ 2.29us-gaap_EarningsPerShareBasic	$ 1.88us-gaap_EarningsPerShareBasic	$ 1.39us-gaap_EarningsPerShareBasic
Fully diluted earnings per common share:
Weighted average number of shares outstanding: (in shares)	67,056,456	67,314,859	67,313,963
Net income (in dollars per share)	$ 2.28us-gaap_EarningsPerShareDiluted	$ 1.88us-gaap_EarningsPerShareDiluted	$ 1.39us-gaap_EarningsPerShareDiluted

Interest expense incurred during the reporting period on other borrowings not defined elsewhere in the taxonomy. Includes interest expense incurred on both the short-term and long-term borrowings (advances) with the Federal Home Loan Bank and other short term borrowings.

No definition available.