Description of Business and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014 Customer Segment	Dec. 31, 2013	Dec. 31, 2012
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Maturity period of highly liquid investments to be considered as cash equivalents		three months or less
Impairment on long-lived assets		$ 0
Amortization of Deferred Revenue		1,080,000	339,000
License Period	25 years
Rental income	60,000
Expiration year of license		2038-12
Rental payment receivable description		The Company entered into a 25 year license for use of the Company's right of way for utility infrastructure, in which the Company received one-half the rental payments in advance
Account receivable from license agreement	5,727,000	5,007,000	5,727,000
Number of major customers		10
Options outstanding for the purchase of common stock	67,082,000	63,285,000	67,082,000	64,547,000
Number of shares relating to options included in the calculation of diluted earnings per share		11,445	12,591
Preferred stock convertible into common stock at rate of shares of common stock	64,000	64,000	64,000
Number of reporting segment		1
Maximum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Percentage of Reimbursement of cost incurred		100.00%
Minimum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Percentage of Reimbursement of cost incurred		65.00%
Threshold revenue of entity wide revenue major customer percentage			10.00%
Minimum [Member] | Freight Operating Revenues [Member] | Customer Concentration Risk [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Company's freight operating revenue by customer			10.00%
Licensing Agreements [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Account receivable from license agreement		$ 750,000