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Note 12 - Employee Benefit Plans (Details Textual) - 401(k) Retirement Plan [Member] $ in Millions | 12 Months Ended
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Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
UNITED STATES |  |  |
Minimum Number Of Employee Working Hours Required To Be Eligible To Participate In 401K Plan | 20 |  |
Minimum Service Period Of Employees To Avail Benefit Under Defined Contribution Benefit Plan | 90 days |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent | 50.00% |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount | $ 2.7 | $ 1.9 | $ 1.6
UNITED KINGDOM |  |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount | $ 0.3 | $ 0.3 | $ 0.2

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- Definition Minimum Number of Employee Working Hours Required to be Eligible to Participate in 401(k) Plan + References No definition available. + Details
Name: | prlb_MinimumNumberOfEmployeeWorkingHoursRequiredToBeEligibleToParticipateInFourZeroOneKPlan
Namespace Prefix: | prlb_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Minimum Service Period Of Employees To Avail Benefit Under Defined Contribution Benefit Plan + References No definition available. + Details
Name: | prlb_MinimumServicePeriodOfEmployeesToAvailBenefitUnderDefinedContributionBenefitPlan
Namespace Prefix: | prlb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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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
Name: | us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_RetirementPlanTypeAxis=prlb_The401KRetirementPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RetirementPlanSponsorLocationAxis=country_US
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RetirementPlanSponsorLocationAxis=country_GB
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |