Statement of Cash Flow Information (Non-Cash Additions and Non-Cash Revenue) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Non-monetary Transaction
Non-monetary exchanges related to resale licensing	$ 2,075	$ 1,840	$ 9,300
Non-monetary exchanges from underwriting of new data acquisition	0	408	0
Adjustment to prior year non-monetary exchanges	(11)	0	(2)
Non-monetary exchanges related to data processing and reproduction services	0	392	13
Total non-cash additions to seismic data library	2,064	2,640	9,311
Non-cash revenue	1,620	3,308	6,928
Acquisition revenue on underwriting [Member]
Non-monetary Transaction
Non-cash revenue	279	129	168
Licensing revenue from specific data licenses and selections [Member]
Non-monetary Transaction
Non-cash revenue	1,250	3,179	6,747
Solutions revenue [Member]
Non-monetary Transaction
Non-cash revenue	$ 91	$ 0	$ 13