Income Taxes - Net Deferred Income Tax Provision (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Depreciation	$ 222	$ 213
Deferred grant income	65	(339)
Track maintenance credit	216	1,123
Accrued casualty and other claims	87	19
Accrued compensated time off and related payroll taxes	16	(17)
Share based compensation	(30)	(41)
Other	18	(167)
Change in valuation allowance	(216)	(852)
Deferred Income Tax Expense (Benefit)	$ 378	$ (61)