Leases - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Leased Assets [Line Items]
Sublease income				$ 5,031	$ 1,816	$ 208
Rent expense for all operating leases				$ 23,757	$ 24,116	$ 22,542
Scenario, Forecast | Railroad Equipment
Operating Leased Assets [Line Items]
Sublease income	$ 71	$ 301	$ 4,872