Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Apr. 30, 2014
Deferred tax assets:
Loan reserves	$ 62,603	$ 72,125
Stock-based compensation plans	10,216	16,471
Deferred revenue	782	793
Operating loss carryovers	4,186	8,371
Unrealized losses	0	5,364
Accrued expenses not currently deductible	5,356	13,605
Unrecorded tax benefits	3,781	5,702
Other	2,410	10,844
Total deferred tax assets	89,334	133,275
Deferred tax liabilities:
Gains on repurchased debt	40,175	126,403
Fixed assets	5,303	6,831
Acquired intangible assets	4,595	6,288
Unrealized gains	1,104	0
Federal deferred for state receivable	3,584	2,058
Other	1,349	875
Total deferred tax liabilities	56,110	142,455
Net deferred tax assets	$ 33,224
Net deferred tax liabilities		$ 9,180	$ 283,000