Description of Business and Summary of Accounting Policies - Additional Information (Detail)		12 Months Ended
	Mar. 01, 2018 USD ($)	Dec. 31, 2018 USD ($) Segment Customer	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Description of Business and Summary of Significant Accounting Policies [Line Items]
Number of operating segments | Segment		1
Depreciation		$ 100,800,000	$ 85,700,000	$ 74,500,000
Primary payroll-related costs capitalized		1,100,000	2,100,000	1,600,000
Workers' compensation discount, amount		$ 5,000,000	3,500,000
Stock-based awards compensation expense amortization period		3 years
Advertising costs		$ 3,900,000	2,200,000	$ 1,200,000
Product Concentration Risk [Member] | Sales Revenue, Net [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Number of customers | Customer		0
Percentage of consolidated operating revenue		5.00%
Restricted Stock [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Stock-based awards compensation expense amortization period		3 years
New Auto Liability Policy [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
New auto liability policy, effective date	Mar. 01, 2018
New auto liability policy, term	3 years
Risk retention amount per occurrence remains under new policy	$ 2,000,000
Provisional extended term of policy	12 months
Accrued additional premium		$ 0
Policy description		Effective March 1, 2018, the Company entered into a new auto liability policy with a three-year term. The risk retention amount per occurrence remains at $2.0 million under the new policy. The policy includes a limit for a single loss of $8.0 million, an aggregate loss limit of $24.0 million for each policy year, and a $48.0 million aggregate loss limit for the 36-month term ended March 1, 2021. The policy includes a returnable premium of up to $5.2 million, to be adjusted by the insurer for changes in claims, and a provision to extend the term of the policy for one additional 12-month period, if management and the insurer mutually agree to commute the policy for the first 12 months of the policy term. A decision with respect to commutation of the first 12 months of the policy cannot be made before March 1, 2019. The policy also includes a returnable premium of up to $15.6 million, to be adjusted by the insurer for changes in claims, if management and the insurer mutually agree to commute the policy for the entire 36 months. A decision with respect to commutation of the entire policy cannot be made before August 30, 2021, unless both the Company and the insurance carrier agree to a commutation prior to the end of the policy term. Additionally, the Company may be required to pay an additional premium of up to $11.0 million if paid losses are greater than $15.6 million over the three-year policy period.
Trailers [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Assets acquired under capital lease, gross		$ 132,500,000	106,300,000
Assets acquired under capital lease, accumulated depreciation		$ 21,600,000	$ 13,300,000
Minimum [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Percentage of revenue derived from transporting		97.00%
Average transit time		1 day
Minimum [Member] | Restricted Stock [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Stock-based awards compensation expense amortization period		3 years
Minimum [Member] | New Auto Liability Policy [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Paid losses specified limit to pay additional premium	$ 15,600,000
Minimum [Member] | ASU No. 2016-02 [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Expected additional operating liabilities to be recognized		$ 70,000,000
Maximum [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Average transit time		5 days
Maximum [Member] | Restricted Stock [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Stock-based awards compensation expense amortization period		5 years
Maximum [Member] | New Auto Liability Policy [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Single loss limit	8,000,000
Aggregate loss limit for each policy year	24,000,000
Aggregate loss limit during policy period	48,000,000
Additional premium to be paid, if paid losses are greater than limit specified	11,000,000
Maximum [Member] | New Auto Liability Policy [Member] | First 12 months [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Returnable premium for changes in claims	5,200,000
Maximum [Member] | New Auto Liability Policy [Member] | Entire 36 Months [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Returnable premium for changes in claims	$ 15,600,000
Maximum [Member] | ASU No. 2016-02 [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Expected additional operating liabilities to be recognized		$ 80,000,000