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Stockholders' Equity - Additional Detail (Details) (USD $)
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Class of Stock [Line Items]    
Total net transfers from the entity that is now a subsidiary of Navient $ 0slm_NetTransfersToFromAffiliate $ 17,244,000slm_NetTransfersToFromAffiliate
Common Stock    
Class of Stock [Line Items]    
Common stock closing price (usd per share) $ 9.28us-gaap_SharePrice
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonStockMember