Annual report pursuant to Section 13 and 15(d)

Related Parties - Additional Information (Detail)

v3.8.0.1
Related Parties - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Sonic Financial Corporation [Member]      
Related Party Transaction [Line Items]      
Aggregate annual rent for leased aircraft usage $ 0.4 $ 0.5 $ 0.6
Oil Chem Research Company [Member]      
Related Party Transaction [Line Items]      
Purchase from related party 1.9 2.1 2.1
SMISC Holdings, Inc. [Member]      
Related Party Transaction [Line Items]      
Purchase from related party 0.9 0.9 0.9
Speedway Motorsports, Inc. [Member]      
Related Party Transaction [Line Items]      
Vehicle sales to related party $ 0.2 $ 0.2 $ 0.1
Minimum [Member] | Mr. Marcus G. Smith [Member] | Sonic Financial Corporation [Member]      
Related Party Transaction [Line Items]      
Ownership percentage 10.00%