Supplemental Cash Flow Information and Non-Cash Activity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash paid during the period for:
Interest	$ 1,039	$ 206
Income taxes	546	819
Non-cash items from investing and financing activities:
Investment in multi-client data library in accounts payable and accrued expenses	0	1,654
Purchases of property, plant, and equipment financed through accounts payable	$ 0	$ 730