Industry Segments - Revenue by type of service (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) category	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Revenue from External Customer
Number of Revenue Categories by Type of Service | category									2
Revenue	$ 21,942	$ 24,013	$ 23,700	$ 20,595	$ 35,001	$ 23,255	$ 24,340	$ 11,950	$ 90,250	$ 94,546	$ 100,252
Acquisition and licensing of seismic data [Member]
Revenue from External Customer
Revenue									88,158	92,454	97,938
Reproduction and delivery of seismic data and other services [Member]
Revenue from External Customer
Revenue									$ 2,092	$ 2,092	$ 2,314