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Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Employee Benefit Plans [Line Items] |  |  |
Minimum service period required | 1 year |  |
Expense of employee related plan | $ 0.8 | $ 0.8 | $ 0.6
Matching Contribution up to 3% [Member] |  |  |
Employee Benefit Plans [Line Items] |  |  |
Matching contribution | 100.00% | 100.00% | 100.00%
Matching Contribution 3 to 5% [Member] |  |  |
Employee Benefit Plans [Line Items] |  |  |
Matching contribution | 50.00% | 50.00% | 50.00%
Employee Contribution Matched at 100% [Member] |  |  |
Employee Benefit Plans [Line Items] |  |  |
Employee contribution | 3.00% | 3.00% | 3.00%
Employee Contribution Matched at 50% [Member] |  |  |
Employee Benefit Plans [Line Items] |  |  |
Employee contribution | 2.00% | 2.00% | 2.00%

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- Definition The minimum required service period in order to qualify for participation in the retirement plan. + References No definition available. + Details
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Data Type: | xbrli:durationItemType
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- Definition Employee Benefit Plans [Line Items] + References No definition available. + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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 Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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- Definition Percentage employer matches of the employee's percentage contribution matched. + References No definition available. + Details
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- Details
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- Details
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- Details
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- Details
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