Supplemental Cash Flow Information and Non-Cash Activity (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash paid during the period for:
Interest	$ 7,273	$ 8,819
Income taxes	3,756	2,579
Non-cash items from investing and financing activities:
Investment in multi-client data library in accounts payable and accrued expenses	8,485	0
Bond exchange	$ 0	$ 10,740