Amtrak Agreement - Schedule of Remaining Track Mileage Credit (Detail) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Agreement With Related Party [Abstract]
Mileage credit available	$ 905,000	$ 418,000	$ 1,200,000
Utilized	199,000	418,000	494,000
Mileage credit remaining	$ 706,000	$ 0	$ 706,000