Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Apr. 30, 2014
Deferred tax assets:
Loan reserves	$ 45,082	$ 33,570
Stock-based compensation plans	16,939	16,342
Deferred revenue	209	418
Operating loss and credit carryovers	16,106	14,324
Unrealized losses	9,949	7,185
Accrued expenses not currently deductible	10,696	10,606
Unrecorded tax benefits	15,251	19,798
Other	9,871	8,918
Total deferred tax assets	124,103	111,161
Deferred tax liabilities:
Gains on repurchased debt	190,936	251,671
Fixed assets	6,237	5,849
Acquired intangible assets	6,724	6,151
Student loan premiums and discounts, net	0	3,050
Other	1,794	2,656
Total deferred tax liabilities	205,691	269,377
Net deferred tax (liabilities) assets	$ (81,588)	$ (158,216)	$ (283,000)