Segment Geographic and Market Information (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net sales by source
Net sales of tangible goods									$ 709,020	$ 636,562	$ 522,530
Services revenues									205,162	167,927	136,694
Freight revenue									28,187	36,548	32,640
Total	233,661	248,044	242,876	217,788	219,387	228,822	218,825	174,003	942,369	841,037	691,864
Cost of sales
Cost of tangible goods sold									511,026	467,431	382,500
Cost of services rendered									156,422	125,997	95,982
Cost associated with freight revenue									22,046	30,683	27,112
Total									$ 689,494	$ 624,111	$ 505,594