Leases - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Leased Assets [Line Items]
Sublease income				$ 3,040	$ 4,778	$ 5,031
Rent expense for all operating leases				$ 20,310	$ 22,040	$ 23,757
Scenario, Forecast | Railroad Equipment
Operating Leased Assets [Line Items]
Sublease income	$ 440	$ 2,853	$ 3,933