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Employee Benefit Plans and Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | May 28, 2015
Maximum employee contribution percentage |  | 75.00% |  |  |
Employer matching contribution percentage |  | 50.00% |  |  |
Employee contribution percentage |  | 4.00% |  |  |
Total matching contributions |  | $ 2.6 |  |  |
Number of shares authorized in ESPP |  | 1,500,000 |  |  |
Maximum payroll deductions, percentage |  | 10.00% |  |  |
Employee purchase price floor, percentage |  | 85.00% |  |  |
Offering period (months) |  | 12 months |  |  |
Offering periods, frequency (months) |  | 6 months |  |  |
Number of purchase periods within an offering period |  | 2 |  |  |
Purchase Period Months |  | 6 months |  |  |
Purchase date, frequency (months) |  | 6 months |  |  |
Purchases of treasury stock, shares (in shares) |  | 800,000 |  |  |
Purchases of treasury stock | $ 0.0 | $ 100.0 | $ 0.0 |  |
Shares reserved for issuance |  |  |  |  | 4,000,000
In-the-money options, maximum exercise price |  | $ 119.80 |  |  |
Options in-the-money, number |  | 100,000 |  |  |
Unrecognized compensation cost |  | $ 126.5 |  |  |
Restricted Stock |  |  |  |  |
Total fair value of RSUs vested | $ 144.5 | $ 120.9 |  | $ 150.0 |
Restricted Stock | Minimum |  |  |  |  |
Vesting period, years |  | 3 years |  |  |
2015 Employee Stock Purchase Plan |  |  |  |  |
Issuance of common stock for Employee Stock Purchase Plan, shares |  | 189,904 | 122,857 | 99,192 |
Shares reserved for issuance |  | 1,100,000 |  |  |
2005 Employee Stock Purchase Plan |  |  |  |  |
Issuance of common stock for Employee Stock Purchase Plan, shares |  |  |  | 8,539 |

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- Definition Employee Stock Purchase Plan (ESPP), Number Of Shares Authorized + References No definition available. + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Definition Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan. + References No definition available. + Details
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- Definition Unrecognized cost of unvested share-based compensation awards. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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