Capital lease obligation period.

No definition available.

Name:	saia_CapitalLeaseObligationPeriod
Namespace Prefix:	saia_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument maximum authorized value.

+ References

No definition available.

+ Details

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Namespace Prefix:	saia_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line of credit facility additional borrowing capacity.

+ References

No definition available.

+ Details

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Namespace Prefix:	saia_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line of credit facility amended expiration month and year.

+ References

No definition available.

+ Details

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Namespace Prefix:	saia_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility expiration year and month.

+ References

No definition available.

+ Details

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Namespace Prefix:	saia_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal, through the balance sheet date and due to be paid more than one year (or one operating cycle, if longer) after the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45023-112735

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

+ References

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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

- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20, 22
-Article 5

+ Details

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

- Definition

Weighted average interest rate of long-term debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_LongtermDebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=saia_FifthAmendedAndRestatedCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=saia_CreditAgreementBeforeAmendmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=saia_RestatedCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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- Details

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- Details

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- Details

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- Details

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Debt and Financing Arrangements - Additional Information (Detail) - USD ($)		3 Months Ended
	Mar. 06, 2015	Mar. 31, 2016	Dec. 31, 2015	Jan. 31, 2008	Nov. 30, 2007	Apr. 30, 2005	Sep. 20, 2002
Debt Instrument [Line Items]
Letter of credit facility outstanding amount		$ 1,800,000
Capital Leases, described below		$ 48,793,000	$ 40,152,000
Lease expiration period		7 years
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Weighted average interest rate for capital lease		2.82%	2.85%
Credit Agreement with Banks [Member]
Debt Instrument [Line Items]
Credit Agreement with Banks		$ 53,360,000	$ 14,534,000
Fifth Amended and Restated Credit Agreement [Member]
Debt Instrument [Line Items]
Amendment line of credit facility expiration year and month	2020-03
Fifth Amended and Restated Credit Agreement [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowing capacity under credit agreement	$ 250,000,000
Fifth Amended and Restated Credit Agreement [Member] \| Revolving Credit Facility [Member] \| Credit Agreement Before Amendments [Member]
Debt Instrument [Line Items]
Borrowing capacity under credit agreement	$ 200,000,000
Restated Credit Agreement [Member]
Debt Instrument [Line Items]
Letter of credit facility outstanding amount		$ 37,900,000	44,800,000
Restated Credit Agreement [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Letter of credit unused portion fee		0.20%
Restated Credit Agreement [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Letter of credit unused portion fee		0.30%
Restated Credit Agreement [Member] \| LIBOR Rate Margin [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Rate margin		1.125%
Restated Credit Agreement [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowing capacity under credit agreement		$ 250,000,000
Line of credit facility expiration year and month		2020-03
Additional borrowing capacity under revolving credit facility		$ 75,000,000
Restated Credit Agreement [Member] \| Credit Agreement with Banks [Member]
Debt Instrument [Line Items]
Credit Agreement with Banks		$ 53,360,000	$ 14,534,000
Restated Credit Agreement [Member] \| Credit Agreement with Banks [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Rate margin		1.125%
Restated Credit Agreement [Member] \| Credit Agreement with Banks [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Rate margin		2.25%
Restated Credit Agreement [Member] \| Credit Agreement with Banks [Member] \| LIBOR Rate Margin [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Rate margin		2.25%
Restated Credit Agreement [Member] \| Credit Agreement with Banks [Member] \| Base Rate Margin [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Rate margin		0.125%
Restated Credit Agreement [Member] \| Credit Agreement with Banks [Member] \| Base Rate Margin [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Rate margin		0.50%
Restated Master Shelf Agreement [Member] \| Senior Notes under Master Shelf Agreement [Member]
Debt Instrument [Line Items]
Senior notes issued, value				$ 25,000,000	$ 25,000,000		$ 100,000,000
Senior notes authorized amount						$ 150,000,000	$ 125,000,000
Interest rate on notes				6.17%	6.14%		7.38%
Senior credit facility, Interest rate terms description		The initial $100 million Senior Notes had a fixed interest rate of 7.38 percent. Payments due under the $100 million Senior Notes were interest only until June 30, 2006 and at that time semi-annual principal payments began with the final payment made in December 2013. The November 2007 issuance of $25 million Senior Notes has a fixed interest rate of 6.14 percent. The January 2008 issuance of $25 million Senior Notes has a fixed interest rate of 6.17 percent. Payments due for both $25 million issuances were interest only until June 30, 2011 and at that time semi-annual principal payments began with the final payments due January 1, 2018.