Loans Held for Investment - Additional Information (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Jul. 01, 2006	Jun. 30, 2006	Sep. 30, 1993
Receivables [Abstract]
Percent of Private Loans indexed to LIBOR	82.00%
Tier 1 of government guarantee	97.00%		97.00%
Tier 2 of government guarantee				98.00%
Tier 3 of government guarantee					100.00%
Estimated weighted average life of student loans	6 years 3 months 8 days	6 years 2 months 8 days