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Debt - Additional Information (Detail) $ / shares in Units, shares in Millions |  |  | 12 Months Ended
--- | --- | --- | ---
Dec. 12, 2016 USD ($) d $ / shares shares | Apr. 27, 2015 USD ($) | Dec. 31, 2017 USD ($) $ / shares shares | Dec. 31, 2016 USD ($) shares | Dec. 31, 2015 USD ($) shares
Debt Instrument |  |  |  |  |
Debt instrument, net proceeds after issuance costs |  |  |  | $ 450,800,000 |
Repurchase of common stock |  |  | $ 200,304,000 | $ 146,331,000 | $ 299,949,000
Repurchase of stock, shares | shares |  |  |  | 6.8 | 15.6
Term of loan, years |  | 5 years |  |  |
Pledge percentage of capital stock |  | 65.00% |  |  |
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 |  |  |  |  |
Debt Instrument |  |  |  |  |
Aggregate principal amount | $ 460,000,000 |  | $ 460,000,000 | $ 460,000,000 |
Debt instrument, interest rate, stated percentage | 1.25% |  |  |  |
Debt instrument, net proceeds after issuance costs | $ 450,800,000 |  |  |  |
Payment for net cost of convertible note hedges net of warrant proceeds | 33,000,000 |  |  |  |
Repurchase of common stock | $ 50,100,000 |  |  |  |
Repurchase of stock, shares | shares | 2.0 |  |  |  |
Senior notes maturity date | Dec. 15, 2023 |  |  |  |
Debt instrument, frequency of periodic payment | Payable semiannually in arrears on June 15 and December 15 of each year |  |  |  |
Debt instrument, date of first required payment | Jun. 15, 2017 |  |  |  |
Debt instrument, conversion option expiration date | Sep. 15, 2023 |  |  |  |
Debt instrument conversion price | $ / shares | $ 31.80 |  | $ 31.80 |  |
Shares that would be issued upon conversion | shares |  |  | 14.5 |  |
Strike price per share of warrant | $ / shares |  |  | $ 39.91 |  |
Debt instrument, convertible, carrying amount of equity component | $ 100,800,000 |  | $ 100,800,000 |  |
Debt instrument, effective annual interest rate |  |  | 5.00% |  |
Financing cost | $ 7,200,000 |  | $ 6,300,000 |  |
Debt issuance costs, amortization period |  |  | 7 years |  |
Unamortized discount |  |  | $ 94,000,000 |  |
Debt Instrument, convertible, remaining discount amortization period |  |  | 6 years |  |
Value of notes converted |  |  | $ 605,700,000 |  |
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 | Conversion option one |  |  |  |  |
Debt Instrument |  |  |  |  |
Trading days measurement period | d | 20 |  |  |  |
Consecutive trading days measurement period | d | 30 |  |  |  |
Percentage of conversion price | 130.00% |  |  |  |
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 | Conversion option two |  |  |  |  |
Debt Instrument |  |  |  |  |
Trading days measurement period | d | 5 |  |  |  |
Consecutive trading days measurement period | d | 5 |  |  |  |
Percentage of closing sale price of common stock and conversion rate product | 98.00% |  |  |  |
Maximum |  |  |  |  |
Debt Instrument |  |  |  |  |
Aggregate principal amount |  | $ 150,000,000 |  |  |
Commitment fee percentage of unused portion of credit facility |  | 0.35% |  |  |
Minimum |  |  |  |  |
Debt Instrument |  |  |  |  |
Commitment fee percentage of unused portion of credit facility |  | 0.125% |  |  |
Base Rate | Maximum |  |  |  |  |
Debt Instrument |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 1.00% |  |  |
Base Rate | Minimum |  |  |  |  |
Debt Instrument |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 0.00% |  |  |
London Interbank Offered Rate (LIBOR) | Maximum |  |  |  |  |
Debt Instrument |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 2.00% |  |  |
London Interbank Offered Rate (LIBOR) | Minimum |  |  |  |  |
Debt Instrument |  |  |  |  |
Debt instrument, basis spread on variable rate |  | 1.00% |  |  |
Revolving Credit Facility |  |  |  |  |
Debt Instrument |  |  |  |  |
Financing cost |  |  | $ 2,300,000 |  |
Financing cost, amortization term |  |  | 5 years |  |
Revolving Credit Facility | Maximum |  |  |  |  |
Debt Instrument |  |  |  |  |
Credit facility, borrowing capacity |  | $ 350,000,000 |  |  |

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- Definition Expiration, mandatory redemption, or due date, in CCYY-MM-DD format, of the financial instrument issued in exchange for the original debt being converted in a noncash or part noncash transaction. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586 + Details
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