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Income Taxes - Significant Components of Deferred Income Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
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Income Tax Disclosure [Abstract] |  |
Allowance for uncollectible accounts | $ 194,876 | $ 80,056
Reserves and accruals | 59,270 | 45,454
Stock-based compensation | 9,201 | 7,975
Net operating loss carryforward | 25,226 | 28,569
Property and equipment | 26 | 685
Other | 1,197 | 970
Deferred tax assets before valuation allowance | 289,796 | 163,709
Less: Valuation allowance | (2,628) | (2,615)
Deferred tax assets, net of valuation allowance | 287,168 | 161,094
Gross deferred tax liabilities: |  |
Amortization | (286,552) | (258,618)
Accounting method changes | (109,418) | (4,150)
Accrual to cash adjustment | (39) | (31,290)
Other | (489) |
Total deferred tax liabilities | (396,498) | (294,058)
Net deferred tax liability | $ (109,330) | $ (132,964)

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