Finance lease obligation period.

No definition available.

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

- 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_
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- Definition

Maximum leverage ratio.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Minimum debt service coverage ratio.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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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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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Present value of lessee's discounted obligation for lease payments from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918701-209980

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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://fasb.org/us-gaap/role/ref/legacyRef
-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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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

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. 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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

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-Section S99
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-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

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-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-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

Weighted average interest rate of long-term debt outstanding calculated at point in time.

+ 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:
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Balance Type:
Period Type:

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
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Balance Type:
Period Type:

- Details

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- Details

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- Details

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Debt and Financing Arrangements - Additional Information (Detail) - USD ($)			9 Months Ended
	Feb. 05, 2019	Mar. 06, 2015	Sep. 30, 2019	Feb. 04, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Letter of credit facility outstanding amount			$ 1,800,000
Finance lease liability			$ 95,260,000		$ 102,859,000
Lease expiration period			7 years
Finance Lease Obligations [Member]
Debt Instrument [Line Items]
Weighted average interest rates for finance lease			3.40%		3.40%
Restated Credit Agreement [Member]
Debt Instrument [Line Items]
Amendment line of credit facility expiration year and month	2024-02
Revolving Credit Facility [Member] \| Restated Credit Agreement [Member]
Debt Instrument [Line Items]
Borrowing capacity under credit agreement	$ 300,000,000
Amendment line of credit facility expiration year and month		2020-03
Additional borrowing capacity under revolving credit facility	$ 100,000,000		$ 75,000,000
Minimum debt service coverage ratio	125.00%
Maximum leverage ratio	325.00%
Credit Agreement with Banks			70,000,000.0		$ 20,000,000.0
Letter of credit facility outstanding amount			$ 26,100,000		$ 27,700,000
Revolving Credit Facility [Member] \| Restated Credit Agreement [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Borrowing capacity under credit agreement		$ 250,000,000
Rate margin	2.00%		2.25%
Letter of credit unused portion fee	0.30%		0.30%
Revolving Credit Facility [Member] \| Restated Credit Agreement [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Rate margin	1.00%		1.125%
Letter of credit unused portion fee	0.175%		0.20%
Revolving Credit Facility [Member] \| Restated Credit Agreement [Member] \| LIBOR Rate Margin [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Rate margin	2.00%		2.25%
Revolving Credit Facility [Member] \| Restated Credit Agreement [Member] \| LIBOR Rate Margin [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Rate margin	1.00%		1.125%
Revolving Credit Facility [Member] \| Restated Credit Agreement [Member] \| Base Rate Margin [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Rate margin	0.50%		0.50%
Revolving Credit Facility [Member] \| Restated Credit Agreement [Member] \| Base Rate Margin [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Rate margin	0.50%		0.125%
Revolving Credit Facility [Member] \| Credit Agreement [Member] \| Credit Agreement Before Amendments
Debt Instrument [Line Items]
Borrowing capacity under credit agreement				$ 250,000,000