Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment
Gross	$ 271,480	$ 284,647
Less accumulated depreciation	(232,580)	(231,098)
Property and equipment, net	38,900	53,549
Land, building and other
Property, Plant and Equipment
Gross	$ 16,070	$ 16,612
Land, building and other | Minimum
Property, Plant and Equipment
Estimated useful lives of property and equipment (in years)	3 years	3 years
Land, building and other | Maximum
Property, Plant and Equipment
Estimated useful lives of property and equipment (in years)	40 years	40 years
Recording equipment
Property, Plant and Equipment
Gross	$ 158,619	$ 163,564
Recording equipment | Minimum
Property, Plant and Equipment
Estimated useful lives of property and equipment (in years)	5 years	5 years
Recording equipment | Maximum
Property, Plant and Equipment
Estimated useful lives of property and equipment (in years)	10 years	10 years
Vibrator energy sources
Property, Plant and Equipment
Gross	$ 73,852	$ 78,626
Vibrator energy sources | Minimum
Property, Plant and Equipment
Estimated useful lives of property and equipment (in years)	5 years	5 years
Vibrator energy sources | Maximum
Property, Plant and Equipment
Estimated useful lives of property and equipment (in years)	15 years	15 years
Vehicles
Property, Plant and Equipment
Gross	$ 22,939	$ 25,845
Vehicles | Minimum
Property, Plant and Equipment
Estimated useful lives of property and equipment (in years)	1 year 6 months	1 year 6 months
Vehicles | Maximum
Property, Plant and Equipment
Estimated useful lives of property and equipment (in years)	10 years	10 years