Additional basic contribution to savings plan by employees in percentage.

No definition available.

Name:	gti_AdditionalBasicContributionToSavingsPlanByEmployeesInPercentage
Namespace Prefix:	gti_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Basic contribution to savings plan by employees in percentage.

+ References

No definition available.

+ Details

Name:	gti_BasicContributionToSavingsPlanByEmployeesInPercentage
Namespace Prefix:	gti_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined benefit plan option for employees to remain for maximum additional period.

+ References

No definition available.

+ Details

Name:	gti_DefinedBenefitPlanOptionForEmployeesToRemainForMaximumAdditionalPeriod
Namespace Prefix:	gti_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Employee Contribution Percent

+ References

No definition available.

+ Details

Name:	gti_EmployeeContributionPercent
Namespace Prefix:	gti_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Employee retirement age.

+ References

No definition available.

+ Details

Name:	gti_EmployeeRetirementAge
Namespace Prefix:	gti_
Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of equity in GTI.

+ References

No definition available.

+ Details

Name:	gti_PercentageOfEquityInGti
Namespace Prefix:	gti_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of increase in salaries based on the final average wages.

+ References

No definition available.

+ Details

Name:	gti_PercentageOfIncreaseInSalariesBasedOnFinalAverageWages
Namespace Prefix:	gti_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of quarterly contributions to each employee's total eligible pay.

+ References

No definition available.

+ Details

Name:	gti_PercentageOfQuarterlyContributionsToEachEmployeesTotalEligiblePay
Namespace Prefix:	gti_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Units of fund that invest in our common stock.

+ References

No definition available.

+ Details

Name:	gti_UnitsOfFundThatInvestInOurCommonStockPercentage
Namespace Prefix:	gti_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The value of a trust established to hold the stock of an employee compensation and benefits plan as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_CompensationAndBenefitsTrust
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Accumulated Benefit Obligation
-URI http://asc.fasb.org/extlink&oid=6503844

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

- Definition

The amount of decrease that relates to an irrevocable action that relieves the employer (or the plan) of primary responsibility for a benefit obligation and eliminates significant risks related to the obligation and the assets used to effect the settlement. Examples of transactions that constitute a settlement include (a) making lump-sum cash payments to plan participants in exchange for their rights to receive specified benefits and (b) purchasing nonparticipating annuity contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 30
-Section 15
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=7577095&loc=d3e8001-114927

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(10)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanSettlementsBenefitObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Target allocation of investments of this type to total plan assets presented on a weighted average basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)(i)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2446-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

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

- Definition

The amount of cash or cash equivalents contributed during the reporting period by the entity to fund its pension plans and its non-pension postretirement benefit plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3536-108585

+ Details

Name:	us-gaap_PensionAndOtherPostretirementBenefitContributions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan.

+ References

No definition available.

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesEmployeeBenefitPlan
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Value of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan.

+ References

No definition available.

+ Details

Name:	us-gaap_StockIssuedDuringPeriodValueEmployeeBenefitPlan
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=gti_FirstOfEmployeeContributionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=gti_NextOfEmployeeContributionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_UnitedStatesPensionPlansOfUSEntityDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Retirement Plans And Postretirement Benefits (Narrative) (Details) $ in Millions		12 Months Ended
	Mar. 27, 2015 USD ($)	Dec. 31, 2015 USD ($) years shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) shares
Defined Benefit Plan Disclosure [Line Items]
Percentage of increase in salaries based on the final average wages		6.00%
Percentage of equity in GTI		50.00%
Option to remain in defined benefit plan for an additional period, in years		5 years
Percentage of quarterly contributions to each employee's total eligible pay		1.00%
Pension and other postretirement benefit contributions		$ 0.6	$ 0.8	$ 0.9
Projected benefit obligations settled	$ 62.0
Defined benefit plan, accumulated benefit obligation		$ 158.9	237.0
Employee retirement age, years \| years		65
Assets of trust approximately		$ 0.8	$ 5.2
Basic contribution to savings plan by employees in percentage		5.00%
Additional basic contribution to savings plan by employees in percentage		45.00%
Stock issued during period, shares, employee savings plan \| shares		321,107	581,006	553,298
Stock issued during period, value, employee benefit plan		$ 1.4	$ 4.4	$ 4.6
First Of Employee Contribution [Member]
Defined Benefit Plan Disclosure [Line Items]
Units of fund that invest in our common stock		3.00%	3.00%	3.00%
Employee contribution percent		100.00%	100.00%	100.00%
Next of Employee Contribution [Member]
Defined Benefit Plan Disclosure [Line Items]
Units of fund that invest in our common stock		5.00%	5.00%	5.00%
Employee contribution percent		20.00%	20.00%	20.00%
Equity Securities [Member] \| U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment plan percentage		20.00%
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment plan percentage		100.00%
Fixed Income Securities [Member] \| U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment plan percentage		80.00%