Percentage of employee contributions may be deferred to a defined contribution plan.

No definition available.

Name:	gemp_DefinedContributionPlanEmployeeContributionDeferredPercentage
Namespace Prefix:	gemp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Employee eligibility age criteria under defined contribution plan.

+ References

No definition available.

+ Details

Name:	gemp_DefinedContributionPlanEmployeeEligibilityAge
Namespace Prefix:	gemp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage employer matches of the employee's percentage contribution matched on one's contribution.

+ References

No definition available.

+ Details

Name:	gemp_DefinedContributionPlanEmployerMatchingContributionPercentOfMatchOnOneSContribution
Namespace Prefix:	gemp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage employer matches of the employee's percentage contribution matched on overall contribution.

+ References

No definition available.

+ Details

Name:	gemp_DefinedContributionPlanEmployerMatchingContributionPercentOfMatchOnOverallContribution
Namespace Prefix:	gemp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period which the employer contribution will be vested under defined contribution plan, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	gemp_DefinedContributionPlanEmployerMatchingContributionVestingPercentage
Namespace Prefix:	gemp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of employee contribution vested on contribution made by employee.

+ References

No definition available.

+ Details

Name:	gemp_EmployeeCompensationVestingPercentageOnContribution
Namespace Prefix:	gemp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

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

- Definition

Percentage employer matches of the employee's percentage contribution matched.

+ References

No definition available.

+ Details

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

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Defined Contribution Plan (Details)	3 Months Ended		6 Months Ended		12 Months Ended
Defined Contribution Plan (Details)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) age	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) age	Dec. 31, 2017 USD ($)
Defined Contribution Plan Disclosure [Line Items]
Minimum age of employee to cover under the plan \| age			21		21
Employee compensation deferred percentage			100.00%		100.00%
Employer match of employee contributions of eligible compensation			100.00%		100.00%
Percentage of compensation matched by employer			3.00%		3.00%
Employer match of over all employee contributions of eligible compensation			50.00%		50.00%
Percentage of compensation matched by employer			3.00%
Percentage of employee contribution vested on their contribution			100.00%		100.00%
Employer matches vesting period			6 years		6 years
Amount of discretionary matching contributions on employee deferrals \| $	$ 19,000	$ 29,000	$ 47,000	$ 54,000	$ 100,000	$ 0
Maximum
Defined Contribution Plan Disclosure [Line Items]
Percentage of compensation matched by employer			5.00%		5.00%