Additional basic contribution to savings plan by employees in percentage.

No definition available.

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- Definition

Basic contribution to savings plan by employees in percentage.

+ References

No definition available.

+ Details

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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

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

- Definition

Employee Contribution Percent

+ References

No definition available.

+ Details

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

- Definition

Employee retirement age.

+ References

No definition available.

+ Details

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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

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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

Number of common stock held in a trust that has been set up specifically to accumulate stock for the sole purpose of distribution to participating employees but not yet earned.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 40

-Section 25

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6418455&loc=d3e16701-113920

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- 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=28361610&loc=d3e1928-114920

+ Details

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

- Details

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Balance Type:	na
Period Type:	duration

- Definition

Amount included in accumulated other comprehensive income (AOCI) related to prior service cost (credit) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.

+ References

No definition available.

+ Details

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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 1

-Subparagraph (d)(i)

-URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920

Reference 2: 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=28361610&loc=d3e2446-114920

+ Details

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

- Definition

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

+ References

+ Details

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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=31042434&loc=d3e3536-108585

+ Details

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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

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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

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- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeSecuritiesMember
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- Details

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Retirement Plans And Postretirement Benefits (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 years	Dec. 31, 2013	Dec. 31, 2012
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%gti_PercentageOfEquityInGti
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	$ 0.8	$ 0.9	$ 1.0
Defined benefit plan, accumulated benefit obligation	237.0	213.2
Employee retirement age, years	65gti_EmployeeRetirementAge
Prior service credit from stockholders' equity	0.2
Assets of trust approximately	5.2us-gaap_CompensationAndBenefitsTrust	5.3us-gaap_CompensationAndBenefitsTrust
Common stock held in employee benefit and compensation trusts, shares	80,967	87,206
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	581,006	553,298	433,496
Stock issued during period, value, employee benefit plan	$ 4.4	$ 4.6	$ 4.6
First Of Employee Contribution [Member]
Defined Benefit Plan Disclosure [Line Items]
Units of fund that invest in our common stock	100.00%
Employee contribution percent	3.00%
Next of Employee Contribution [Member]
Defined Benefit Plan Disclosure [Line Items]
Units of fund that invest in our common stock	50.00%
Employee contribution percent	2.00%
Equity Securities [Member] \| U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment plan percentage	20.00%
Investment plan maximum	100.00%
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%