Industry Segments and Geographic Information Industry Segments and Geographic Information 2 (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 227,644	$ 216,364	$ 208,369	$ 168,001	$ 173,222	$ 176,553	$ 175,660	$ 169,329	$ 820,378	$ 694,764	$ 1,130,145
Transfers between geographic areas									(2,025)	(93)	(1,252)
Identifiable assets	1,308,614				1,315,540				1,308,614	1,315,540	1,636,202
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									643,216	535,613	896,131
Transfers between geographic areas									0	0	0
Identifiable assets	1,131,650				1,132,986				1,131,650	1,132,986	1,403,916
Canada and Mexico [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									35,975	34,560	44,542
Transfers between geographic areas									0	0	0
Identifiable assets	62,537				64,163				62,537	64,163	74,260
South America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									28,167	20,480	26,554
Transfers between geographic areas									0	0	0
Identifiable assets	23,352				21,354				23,352	21,354	25,603
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									80,721	71,882	80,432
Transfers between geographic areas									2,025	93	1,252
Identifiable assets	61,000				53,713				61,000	53,713	64,695
Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									700	10,345	20,761
Transfers between geographic areas									0	0	0
Identifiable assets	3,696				5,711				3,696	5,711	7,542
Asia and other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									31,599	21,884	61,725
Transfers between geographic areas									0	0	0
Identifiable assets	26,379				37,613				26,379	37,613	60,186
Eliminations [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Identifiable assets	$ 0				$ 0				$ 0	$ 0	$ 0