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Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Dec. 31, 2015
Income Tax [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax at statutory rate |  |  |  |  |  |  |  |  |  | 21.00% | 35.00% | 35.00% |  |
Effective tax rate |  |  |  |  |  |  |  |  |  | 27.17% | 21.94% | 36.80% |  |
Income tax benefit resulting from the reduction of deferred tax liabilities |  |  |  |  | $ (70,000) |  |  |  |  |  |  |  |  |
Effective income tax rate favorable impact of change in uncertain tax positions |  |  |  |  |  |  |  |  |  |  |  |  | $ 10,600 |
Increase (decrease) in net deferred tax liability |  |  |  |  |  |  |  |  |  | $ (23,600) |  |  |  |
Increase in allowance for uncollectible accounts |  |  |  |  |  |  |  |  |  | 114,800 |  |  |  |
Accounting method changes | $ 109,418 |  |  |  | 4,150 |  |  |  |  | 109,418 | $ 4,150 |  |  |
Decrease in accrual to cash adjustment |  |  |  |  |  |  |  |  |  | 31,300 |  |  |  |
Adjustment to additional paid-in capital for excess tax benefits related to stock-based awards |  |  |  |  |  |  |  |  |  |  |  | $ 4,200 |  |
Income tax expense for excess tax deficiencies |  |  |  |  |  |  |  |  |  | 1,400 | 200 |  |  |
Net operating loss carryforwards for federal and state tax | 101,900 |  |  |  | 116,000 |  |  |  |  | 101,900 | 116,000 | 130,000 |  |
Operating loss carryforwards subject to expiration | 74,300 |  |  |  |  |  |  |  |  | 74,300 |  |  |  |
Operating loss carryforwards not subject to expiration | 27,600 |  |  |  |  |  |  |  |  | 27,600 |  |  |  |
Uncertain tax position liability | 11,185 |  |  |  | 10,972 |  |  |  |  | 11,185 | 10,972 | 9,469 |  | $ 18,447
Unrecognized tax benefits that would impact effective tax rate | 10,900 |  |  |  |  |  |  |  |  | 10,900 |  |  |  |
Increase (decrease) in uncertain tax position |  |  |  |  |  |  |  |  |  | 200 | 1,500 |  |  |
Income tax expense (benefit) | 21,156 | $ 24,873 | $ 30,122 | $ 24,059 | (27,761) | $ 42,119 | $ 40,725 | $ 34,967 |  | 100,210 | 90,050 | 189,203 |  |
Company's accrued liability for interest and penalties related to income tax liabilities | 1,100 |  |  |  | $ 1,200 |  |  |  |  | $ 1,100 | 1,200 |  |  |
Interest and Penalties [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income tax expense (benefit) |  |  |  |  |  |  |  |  |  |  | $ 200 | $ 7,900 |  |
Earliest Tax Year [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal and state income tax examinations |  |  |  |  |  |  |  |  |  | 2014 |  |  |  |
Latest Tax Year [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal and state income tax examinations |  |  |  |  |  |  |  |  |  |  | 2017 |  |  |
Internal Revenue Code Section 481 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounting method changes | $ 105,300 |  |  |  |  |  |  |  |  | $ 105,300 |  |  |  |
Scenario, Forecast [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in uncertain tax position |  |  |  |  |  |  |  |  | $ 200 |  |  |  |  |
Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expiration period of operating loss carryforwards |  |  |  |  |  |  |  |  |  | 2019 |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expiration period of operating loss carryforwards |  |  |  |  |  |  |  |  |  | 2038 |  |  |  |

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