Represents the number every share or unit issued under the plan counts against aggregate share limit.

No definition available.

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- Definition

Represents the exercise price of the purchase right as a percentage of the fair market value of a share of common stock on the first day of the purchase right period.

+ References

No definition available.

+ Details

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- Definition

Represents the exercise price of the purchase right as a percentage of the fair market value of a share of common stock on the last day of the purchase right period.

+ References

No definition available.

+ Details

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- Definition

Represents the maximum amount that an employee is permitted to contribute during a purchase right period.

+ References

No definition available.

+ Details

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 14
-Section F

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- Definition

The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- References

No definition available.

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- 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

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Balance Type:	na
Period Type:	instant

- Definition

Percentage of vesting of share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Balance Type:	na
Period Type:	duration

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Data Type:	xbrli:durationItemType
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Period Type:	duration

- Details

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Namespace Prefix:
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- Details

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- Details

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- Details

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- Details

Name:	us-gaap_VestingAxis=ttek_FirstAnniversaryOfGrantDateAndMonthlyThereafterMember
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- Details

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- Details

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- Details

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Stockholders' Equity and Stock Compensation Plans - Summary (Details) - USD ($)	1 Months Ended	12 Months Ended
	Mar. 31, 2006	Oct. 02, 2016	Sep. 27, 2015	Sep. 28, 2014
Stockholder's equity and stock compensation plans
Vesting period		1 year	1 year
Stock-based compensation and related income tax benefits
Stock-based compensation expense		$ 12,964,000	$ 10,926,000	$ 10,374,000
Income tax benefit related to stock-based compensation		(4,656,000)	(3,811,000)	(3,696,000)
Stock-based compensation, net of tax benefit		$ 8,308,000	$ 7,115,000	6,678,000
RSUs
Stockholder's equity and stock compensation plans
Vesting period		4 years	4 years
ESPP
Stockholder's equity and stock compensation plans
Available for future awards		2,373,290
Maximum amount that an employee can contribute during a purchase right period		$ 5,000
Exercise price as percentage of fair market value on the first day of purchase right period		100.00%
Exercise price as percentage of fair market value on the last day of purchase right period		85.00%
Stock-based compensation and related income tax benefits
Stock-based compensation expense		$ 400,000	$ 600,000	$ 700,000
2005 EIP \| Stock options
Stockholder's equity and stock compensation plans
Expiration period	10 years	8 years
Vesting period	4 years
2005 EIP \| Stock options \| First anniversary of grant date and monthly thereafter
Stockholder's equity and stock compensation plans
Percentage of vesting rights after specified period	25.00%
2005 EIP \| Stock options \| Each anniversary of grant date
Stockholder's equity and stock compensation plans
Percentage of vesting rights after specified period		25.00%
2005 EIP \| RSUs \| Each anniversary of grant date
Stockholder's equity and stock compensation plans
Percentage of vesting rights after specified period		25.00%
2005 EIP \| Restricted Stock
Stockholder's equity and stock compensation plans
Vesting period		3 years
2015 EIP
Stockholder's equity and stock compensation plans
Available for future awards		3,700,000
The number every share or unit issued counts against aggregate share limit		3