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
Operating Leased Assets [Line Items]
Sublease income			$ 4,778	$ 5,031	$ 1,816
Rent expense for all operating leases			$ 22,040	$ 23,757	$ 24,116
Scenario, Forecast | Railroad Equipment
Operating Leased Assets [Line Items]
Sublease income	$ 581	$ 993