CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Retained Earnings Series A Preferred Stock	Retained Earnings Series B Preferred Stock	Total SLM Corporation Equity	Total SLM Corporation Equity Series A Preferred Stock	Total SLM Corporation Equity Series B Preferred Stock
Beginning Balance (in shares) at Dec. 31, 2014		7,300,000	423,438,848	(1,365,277)
Beginning Balance, shares issued (in shares) at Dec. 31, 2014			424,804,125
Beginning Balance at Dec. 31, 2014		$ 565,000	$ 84,961	$ (12,187)	$ 1,090,511	$ (11,393)	$ 113,066			$ 1,829,958
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 47,699						47,699			47,699
Other comprehensive income (loss), net of tax	$ (9,191)					(9,191)				(9,191)
Comprehensive income										38,508
Cash dividends:
Cash dividends, preferred stock								$ (2,875)	$ (1,948)		$ (2,875)	$ (1,948)
Dividend equivalent units related to employee stock-based compensation plans					1,118		(1,118)			0
Issuance of common shares (in shares)	3,130,839		3,130,839
Issuance of common shares			$ 626		4,050					4,676
Tax benefit related to employee stock-based compensation					4,596					4,596
Stock-based compensation expense					6,140					6,140
Shares repurchased related to employee stock-based compensation plans (in shares)			(1,389,096)	(1,389,096)
Shares repurchased related to employee stock-based compensation plans				$ (13,142)						(13,142)
Ending Balance (in shares) at Mar. 31, 2015		7,300,000	425,180,591	(2,754,373)
Ending Balance, shares issued (in shares) at Mar. 31, 2015			427,934,964
Ending Balance at Mar. 31, 2015		$ 565,000	$ 85,587	$ (25,329)	1,106,415	(20,584)	154,824			1,865,913
Beginning Balance (in shares) at Dec. 31, 2015		7,300,000	426,303,244	(4,374,190)
Beginning Balance, shares issued (in shares) at Dec. 31, 2015			430,677,434
Beginning Balance at Dec. 31, 2015	$ 2,096,323	$ 565,000	$ 86,136	$ (41,223)	1,135,860	(16,059)	366,609			2,096,323
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	65,915						65,915			65,915
Other comprehensive income (loss), net of tax	$ (13,210)					(13,210)				(13,210)
Comprehensive income										52,705
Cash dividends:
Cash dividends, preferred stock								$ (2,875)	$ (2,264)		$ (2,875)	$ (2,264)
Dividend equivalent units related to employee stock-based compensation plans					399		(399)			0
Issuance of common shares (in shares)	2,740,979		2,740,979
Issuance of common shares			$ 548		2,159					2,707
Tax benefit related to employee stock-based compensation					(2,132)					(2,132)
Stock-based compensation expense					6,216					6,216
Shares repurchased related to employee stock-based compensation plans (in shares)			(1,128,709)	(1,128,709)
Shares repurchased related to employee stock-based compensation plans				$ (6,755)						(6,755)
Ending Balance (in shares) at Mar. 31, 2016		7,300,000	427,915,514.000	(5,502,899.000)
Ending Balance, shares issued (in shares) at Mar. 31, 2016			433,418,413.000
Ending Balance at Mar. 31, 2016	$ 2,143,925	$ 565,000	$ 86,684	$ (47,978)	$ 1,142,502	$ (29,269)	$ 426,986			$ 2,143,925