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Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2019 | Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Average Balance | $ 23,747,242 | $ 20,108,078
Private Education Loans |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Average Balance | $ 21,732,826 | $ 18,659,717
Weighted Average Interest Rate | 9.50% | 8.84%
FFELP Loans |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Average Balance | $ 837,950 | $ 919,717
Weighted Average Interest Rate | 4.94% | 4.25%
Personal Loans |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Average Balance | $ 1,176,466 | $ 528,644
Weighted Average Interest Rate | 11.81% | 10.64%

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- Definition Loans and Leases Receivable, before Fees, Gross, Average Balance + References No definition available. + Details
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Namespace Prefix: | slm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Weighted Average Interest Rate on Loans + References No definition available. + Details
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Namespace Prefix: | slm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Data Type: | na
Balance Type: |
Period Type: |