Supplemental Cash Flow Information and Non-Cash Activity (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash paid during the period for:
Interest	$ 7,075	$ 8,149
Income taxes (refunds)	2,364	(6)
Non-cash items from investing and financing activities:
Investment in multi-client data library in accounts payable and accrued expenses	4,561	0
Bond exchange	$ 0	$ 10,740