Long-Term Debt - Summary (Details) - USD ($) $ in Thousands		12 Months Ended
	Feb. 08, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 15, 2016	Dec. 31, 2013
Long-term debt
Less current maturities		$ (2,829)	$ (1,629)
Long-term Debt, Excluding Current Maturities, Total		306,726	182,506
Deferred financing costs, net		4,033	2,337	$ 2,485		$ 2,216
Total long-term debt		306,726	182,506
Long-term debt, additional disclosure
Financing costs		2,320		2,132
Inventories - truck chassis floor plan		3,939
Write off of unamortized deferred financing costs				701
Loan modification fees expensed			580
Write off of unamortized debt discount			589
Loss on extinguishment of debt				$ 1,870
Term loan facility
Long-term debt
Term Loan, net of debt discount		313,588	186,472
Less current maturities		2,829	1,629
Long-term Debt, Excluding Current Maturities, Total		310,759	$ 184,843
Total long-term debt		313,588
Schedule of maturities on long-term debt
2017		2,829
2018		2,829
2019		2,829
2020		2,829
2021		302,272
Long-term debt, additional disclosure
Incremental term loan		$ 10,000
Actual interest rate (as a percent)		5.25%	5.25%
Unamortized discount on issuance of debt		$ 1,953	$ 1,629
Financing costs		2,120
Revolving credit facility
Long-term debt, additional disclosure
Financing costs		200
Revolving credit facility | Second option | Fixed rate | Maximum | Subsequent
Long-term debt, additional disclosure
Fixed interest rate base (as a percent)	1.00%
Incremental Term Loan Facility
Long-term debt, additional disclosure
Unamortized discount on issuance of debt		650
Senior credit facilities
Long-term debt, additional disclosure
Floor plan financing arrangements					$ 20,000
Remaining borrowing availability		$ 89,664
Percentage of net cash proceeds of certain asset sales, certain insurance or condemnation events, requirement for additional principal prepayments		100.00%
Percentage of excess cash flow paid as additional principal prepayments		50.00%
Reduced percentage of excess cash flow paid as additional principal prepayments upon achievement of certain leverage ratio thresholds, one		0.00%
Senior credit facilities | Maximum
Long-term debt, additional disclosure
Period before end of the fiscal year, for additional principal prepayments of debt, from excess cash flow		150 days
Senior credit facilities | Term loan facility
Long-term debt, additional disclosure
Maximum borrowing capacity		$ 190,000
Borrowings under senior credit facility		$ 315,540			$ 130,000
Senior credit facilities | Term loan facility | Subsequent
Long-term debt, additional disclosure
Borrowings under senior credit facility	$ 315,500
Senior credit facilities | Term loan facility | Maximum
Long-term debt, additional disclosure
Additional term loan commitments			$ 80,000
Debt ratio			3.25
Senior credit facilities | Term loan facility | ABR
Long-term debt, additional disclosure
Interest rate margin (as a percent)	3.25%
Senior credit facilities | Term loan facility | Euro dollar
Long-term debt, additional disclosure
Interest rate margin (as a percent)	4.25%
Senior credit facilities | Term loan facility | First option | Subsequent
Long-term debt, additional disclosure
Interest rate margin (as a percent)	0.50%
Senior credit facilities | Term loan facility | First option | Minimum
Long-term debt, additional disclosure
Additional fixed interest rate spread (as a percent)			1.00%
Additional interest margin added to fixed and variable rates (as a percent)			1.00%
Senior credit facilities | Term loan facility | First option | Base rate
Long-term debt, additional disclosure
Fixed interest rate base (as a percent)	2.50%
Senior credit facilities | Term loan facility | First option | Federal funds
Long-term debt, additional disclosure
Variable rate basis description		Federal funds
Interest rate margin (as a percent)			0.50%
Senior credit facilities | Term loan facility | First option | Federal funds | Subsequent
Long-term debt, additional disclosure
Variable rate basis description	Federal funds
Senior credit facilities | Term loan facility | First option | Fixed rate
Long-term debt, additional disclosure
Fixed interest rate base (as a percent)			2.50%
Senior credit facilities | Term loan facility | First option | One month London Interbank Offered Rate
Long-term debt, additional disclosure
Variable rate basis description		LIBOR for a one month interest period
Senior credit facilities | Term loan facility | First option | One month London Interbank Offered Rate | Subsequent
Long-term debt, additional disclosure
Variable rate basis description	LIBOR for a one month interest period
Senior credit facilities | Term loan facility | First option | Prime
Long-term debt, additional disclosure
Variable rate basis description		Prime Rate
Senior credit facilities | Term loan facility | First option | Prime | Subsequent
Long-term debt, additional disclosure
Variable rate basis description	Prime Rate
Senior credit facilities | Term loan facility | Second option | Minimum | Subsequent
Long-term debt, additional disclosure
Additional fixed interest rate spread (as a percent)	2.00%
Additional interest margin added to fixed and variable rates (as a percent)	1.00%
Senior credit facilities | Term loan facility | Second option | Base rate | Subsequent
Long-term debt, additional disclosure
Fixed interest rate base (as a percent)	3.50%
Senior credit facilities | Term loan facility | Second option | Fixed rate
Long-term debt, additional disclosure
Additional fixed interest rate spread (as a percent)			1.00%
Fixed interest rate base (as a percent)			3.50%
Senior credit facilities | Revolving credit facility | Second option | Federal funds
Long-term debt, additional disclosure
Variable rate basis description		federal funds
Senior credit facilities | Revolving credit facility | Second option | One month London Interbank Offered Rate
Long-term debt, additional disclosure
Variable rate basis description		LIBOR for a one month interest period
Senior credit facilities | Revolving credit facility | Second option | Prime
Long-term debt, additional disclosure
Variable rate basis description		Prime Rate
Senior credit facilities | Amended term loan facility | ABR | Subsequent
Long-term debt, additional disclosure
Interest rate margin (as a percent)	2.50%
Senior credit facilities | Amended term loan facility | Euro dollar | Subsequent
Long-term debt, additional disclosure
Interest rate margin (as a percent)	3.50%
Letter of Credit
Long-term debt, additional disclosure
Maximum borrowing capacity		$ 10,000
Revolving credit facility
Long-term debt
Total long-term debt		0
Long-term debt, additional disclosure
Maximum borrowing capacity		100,000
Annual acquisitions allowed		$ 12,500
Fixed charge coverage ratio to be maintained if certain minimum availability under the credit facility is not maintained.		1
Revolving credit facility | Maximum
Long-term debt, additional disclosure
Facilities consolidation expenditure allowed		$ 15,000
Revolving credit facility | First option | Fixed rate | Maximum
Long-term debt, additional disclosure
Fixed interest rate base (as a percent)			2.00%
Revolving credit facility | First option | Fixed rate | Minimum
Long-term debt, additional disclosure
Fixed interest rate base (as a percent)			1.50%
Revolving credit facility | Second option | Federal funds
Long-term debt, additional disclosure
Interest rate margin (as a percent)			0.50%
Revolving credit facility | Second option | Federal funds | Maximum
Long-term debt, additional disclosure
Interest rate margin (as a percent)			1.00%
Revolving credit facility | Second option | Federal funds | Minimum
Long-term debt, additional disclosure
Interest rate margin (as a percent)			0.50%
Revolving credit facility | Second option | One month London Interbank Offered Rate
Long-term debt, additional disclosure
Interest rate margin (as a percent)			1.00%
Swingline loan
Long-term debt, additional disclosure
Maximum borrowing capacity		5,000
Prior To Amendment | Senior credit facilities | Term loan facility
Long-term debt, additional disclosure
Borrowings under senior credit facility		100,000
Incremental term loan		$ 5,000