Industry Segments and Geographic Information Industry Segments and Geographic Information 2 (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 315,850	$ 306,371	$ 242,489	$ 212,857	$ 225,435	$ 254,303	$ 221,101	$ 208,559	$ 1,077,567	$ 909,398	$ 880,831	$ 880,831
Transfers between geographic areas									(2,871)	(112)	(172)
Identifiable assets	2,067,836				1,206,533				2,067,836	1,206,533	1,261,818
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									768,688	673,376	625,885
Transfers between geographic areas									0	0	0
Identifiable assets	1,763,805				852,483				1,763,805	852,483	913,080
Canada and Mexico [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									73,632	58,080	85,133
Transfers between geographic areas									0	0	0
Identifiable assets	97,737				104,831				97,737	104,831	116,059
South America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									40,719	31,788	42,482
Transfers between geographic areas									0	0	0
Identifiable assets	32,267				43,326				32,267	43,326	51,858
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									105,457	102,990	92,882
Transfers between geographic areas									2,871	112	172
Identifiable assets	94,209				150,415				94,209	150,415	135,219
Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									22,277	15,127	20,194
Transfers between geographic areas									0	0	0
Identifiable assets	7,895				9,063				7,895	9,063	13,700
Asia and other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									66,794	28,037	14,255
Transfers between geographic areas									0	0	0
Identifiable assets	71,923				46,351				71,923	46,351	31,902
Eliminations [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Identifiable assets	$ 0				$ 64				$ 0	$ 64	$ 0