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Allowance for Loan Losses - Accrued Interest Receivable (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Receivables [Abstract]    
Accrued Interest Receivable On Private Education Loans $ 512,501slm_AccruedInterestReceivableOnPrivateEducationLoans $ 445,710slm_AccruedInterestReceivableOnPrivateEducationLoans
Greater Than 90 Days Past Due 473slm_GreaterThanNinetyDaysPastDueAccruedInterestReceivable 443slm_GreaterThanNinetyDaysPastDueAccruedInterestReceivable
Allowance For Uncollectible Accrued Interest $ 2,634slm_AllowanceForUncollectibleAccruedInterest $ 3,517slm_AllowanceForUncollectibleAccruedInterest