Assets Held for Sale (Narrative) (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) property	Dec. 31, 2016 USD ($) property
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale	$ 25,153	$ 9,634
Period of time assets are expected to be sold, months	12 months
Number of properties sold | property	0	0
Gain on sale of real property	$ 0	$ 0
Land And Facilities [Member]
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale	0
Revenue Equipment [Member]
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale	$ 25,200	$ 9,600