Industry Segments - Geographic information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 Segment		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Number of Operating Segments											1
Revenue	$ 52,351		$ 41,299	$ 47,334	$ 57,053	$ 59,569		$ 44,410	$ 47,544	$ 51,351	$ 198,037		$ 202,874		$ 240,458
Assets (1)	168,936	[1]				200,389	[1]				168,936	[1]	200,389	[1]	184,935	[1]
United States [Member]
Segment Reporting Information [Line Items]
Revenue											156,722		157,819		159,787
Assets (1)	121,424	[1]				123,555	[1]				121,424	[1]	123,555	[1]	105,486	[1]
Canada [Member]
Segment Reporting Information [Line Items]
Revenue											41,315		45,055		80,671
Assets (1)	$ 47,512	[1]				$ 76,834	[1]				$ 47,512	[1]	$ 76,834	[1]	$ 79,449	[1]

[1] Assets include net seismic data library and net property and equipment.