Industry Segments and Geographic Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 225,435	$ 254,303	$ 221,101	$ 208,559	$ 231,140	$ 233,986	$ 234,909	$ 180,796	$ 909,398	$ 880,831	$ 845,275
Transfers between geographic areas									(112)	(172)	(322)
Identifiable assets	1,206,533				1,261,818				1,206,533	1,261,818	1,203,310
US [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									673,376	625,885	671,926
Transfers between geographic areas									0	0	0
Identifiable assets	852,483				913,080				852,483	913,080	994,151
Canada and Mexico [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									58,080	85,133	49,314
Transfers between geographic areas									0	0	0
Identifiable assets	104,831				116,059				104,831	116,059	62,558
South America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									31,788	42,482	28,765
Transfers between geographic areas									0	0	0
Identifiable assets	43,326				51,858				43,326	51,858	43,295
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									102,990	92,882	75,033
Transfers between geographic areas									112	172	322
Identifiable assets	150,415				135,219				150,415	135,219	78,974
Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									15,127	20,194	13,877
Transfers between geographic areas									0	0	0
Identifiable assets	9,063				13,700				9,063	13,700	11,653
Asia and other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									28,037	14,255	6,360
Transfers between geographic areas									0	0	0
Identifiable assets	46,351				31,902				46,351	31,902	12,679
Eliminations [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Identifiable assets	$ 64				$ 0				$ 64	$ 0	$ 0