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Debt - Additional Information (Detail) $ / shares in Units, $ in Thousands, shares in Millions |  | 3 Months Ended | 6 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 12, 2016 USD ($) Customer shares | Jun. 30, 2019 USD ($) $ / shares | Jun. 30, 2019 USD ($) $ / shares | Jul. 01, 2018 USD ($) | Dec. 31, 2018 USD ($) shares | Dec. 31, 2016 USD ($) $ / shares | Apr. 27, 2015 USD ($)
Debt Instrument |  |  |  |  |  |  |
Repurchase of common stock |  |  | $ 247,222 | $ 360,795 |  |  |
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |
Aggregate principal amount | $ 460,000 | $ 460,000 | $ 460,000 |  | $ 460,000 |  |
Debt instrument, interest rate, stated percentage | 1.25% |  |  |  |  |  |
Debt instrument, net proceeds after issuance costs | $ 450,800 |  |  |  |  |  |
Payment for net cost of convertible note hedges net of warrant proceeds | 33,000 |  |  |  |  |  |
Repurchase of common stock | $ 50,100 |  |  |  |  |  |
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 |  | $ 31.70 | $ 31.70 |  |  | $ 31.70 |
Shares that would be issued upon conversion | shares |  |  |  |  | 14.5 |  |
Strike price per share of warrant | $ / shares |  | $ 39.78 |  |  |  |  |
Debt instrument, convertible, carrying amount of equity component |  | $ 100,800 | $ 100,800 |  |  |  |
Financing cost |  | 4,800 | $ 4,800 |  |  | $ 7,200 |
Debt issuance costs, amortization period |  |  | 7 years |  |  |  |
Unamortized discount |  | $ 72,800 | $ 72,800 |  |  |  |
Debt Instrument, convertible, remaining discount amortization period |  |  | 4 years 6 months |  |  |  |
Value of notes converted |  |  | $ 695,200 |  |  |  |
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 | Conversion option one |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |
Trading days measurement period | Customer | 20 |  |  |  |  |  |
Consecutive trading days measurement period | Customer | 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 | Customer | 5 |  |  |  |  |  |
Consecutive trading days measurement period | Customer | 5 |  |  |  |  |  |
Percentage of closing sale price of common stock and conversion rate product | 98.00% |  |  |  |  |  |
Revolving Credit Facility | Maximum |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |
Credit facility, borrowing capacity |  |  |  |  |  |  | $ 350,000

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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://fasb.org/us-gaap/role/ref/legacyRef -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 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
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