Seismic Data Library (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2018
Seismic Data Library [Abstract]
Straight-line amortization period	4 years
Net book value of seismic data library, projects in progress	6.00%	5.00%
Internal data processing costs capitalized	$ 2,600	$ 2,900	$ 3,500
Lowest amortization rate using the income forecast method	70.00%
Amortization of seismic data library	$ 76,500	$ 70,200	$ 75,900
Amortization as percentage of total seismic revenue, rate	87.00%	76.00%	78.00%
Actual aggregate rate of amortization				70.00%
Asset impairment charges	$ 0	$ 0	$ 0