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Income Taxes - Significant Components of Deferred Income Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
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Income Tax Disclosure [Abstract] |  |
Allowance for uncollectible accounts | $ 79,755 | $ 170,123
Reserves and accruals | 64,445 | 54,685
Stock-based compensation | 7,517 | 11,493
Operating loss and other carryforwards | 16,767 | 6,691
Capital loss carryforwards | 447,854 | 17,082
Operating lease assets | 15,042 | 15,389
Property and equipment | 3,044 | 3,986
Other | 571 |
Deferred tax assets before valuation allowance | 634,995 | 279,449
Less: Valuation allowance | (458,708) | (19,286)
Deferred tax assets, net of valuation allowance | 176,287 | 260,163
Gross deferred tax liabilities: |  |
Amortization | (152,969) | (144,587)
Accounting method changes | (16,352) | (71,532)
Operating lease liabilities | (14,057) | (13,405)
Other | (183) | (463)
Total deferred tax liabilities | (183,561) | (229,987)
Net deferred tax assets | $ (7,274) |
Net deferred tax liabilities |  | $ 30,176

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