Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Deferred tax assets:
Loan reserves	$ 376,029	$ 354,412
Net unrealized losses	21,209	24,176
Accrued expenses not currently deductible	19,841	16,297
Unrecorded tax benefits	12,008	11,568
Research and development costs	38,119	26,519
Stock-based compensation plans	12,885	10,847
Acquired intangible assets	16,394	14,536
Operating loss carryovers	0	26
Other	1,785	1,426
Total deferred tax assets	498,270	459,807
Deferred tax liabilities:
Student loan premiums and discounts, net	22,873	15,908
Fixed assets	7,708	8,533
Federal deferred for state receivable	1,908	1,171
Other	402	614
Total deferred tax liabilities	32,891	26,226
Net deferred tax assets	$ 465,379	$ 433,581