Related Parties - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Oil Chem Research Company [Member]
Related Party Transaction [Line Items]
Purchase from related party	$ 2.1	$ 2.0	$ 2.0
SFC [Member]
Related Party Transaction [Line Items]
Aggregate annual rent for leased aircraft usage	0.5	0.9	0.9
Speedway Motorsports, Inc. [Member]
Related Party Transaction [Line Items]
Aggregate annual rent for leased aircraft usage	$ 0.6	$ 0.6	$ 0.4