Amtrak Agreement - Additional Information (Detail) - USD ($)		12 Months Ended
	Apr. 04, 2012	Dec. 31, 2015	Dec. 31, 2014
Dispute Settlement Agreement [Line Items]
Dispute settlement gross amount		$ 418,000	$ 1,219,000
Dispute Settlement Gross Amount Remaining		$ 0	$ 418,000
Amtrak Agreement [Member]
Dispute Settlement Agreement [Line Items]
Dispute settlement gross amount	$ 5,577,000
Amtrak Agreement [Member] | License Arrangement [Member]
Dispute Settlement Agreement [Line Items]
Dispute settlement gross amount	179,000
Amtrak Agreement [Member] | Track Material [Member]
Dispute Settlement Agreement [Line Items]
Dispute settlement gross amount	684,000
Amtrak Agreement [Member] | Inter Entity Outstanding Adjustment [Member]
Dispute Settlement Agreement [Line Items]
Dispute settlement gross amount	2,143,000
Amtrak Agreement [Member] | Mileage Charges Freight [Member]
Dispute Settlement Agreement [Line Items]
Dispute settlement gross amount	$ 2,571,000