Variable Interest Entities - Guarantee and Other Payments Related to PEAKS Program (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Variable Interest Entity [Line Items]
PEAKS Guarantee					$ 159,300
Payments on Behalf of Borrowers					$ 1,832
PEAKS Program [Member]
Variable Interest Entity [Line Items]
PEAKS Guarantee	$ 4,856	$ 52,517	$ 25,313	$ 94,318
Payments on Behalf of Borrowers	0	0	0	1,832
Total	$ 4,856	$ 52,517	$ 25,313	$ 96,150