Supplemental Cash Flow Information and Non-Cash Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash paid during the period for:
Interest	$ 12,381	$ 12,463	$ 14,181
Income taxes	11,065	3,260	7,030
Non-cash items from investing and financing activities:
Purchase of computer equipment financed through capital leases	0	3,297	0
Investment in multi-client data library financed through trade payables and accruals	$ 6,649	$ 4,956	$ 9,059