Segment Information (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
segment
Jun. 30, 2012
Dec. 31, 2012
Segment Reporting Information [Line Items]          
Number of operating segments     2    
Revenues $ 3,417,430 $ 1,702,703 $ 6,637,147 $ 3,419,800  
Cost of revenue 3,152,841 1,580,199 6,124,185 3,186,907  
Gross profit 264,589 122,504 512,962 232,893  
Total assets 7,347,812 1,851,231 7,347,812 1,851,231 7,385,127
P B M
         
Segment Reporting Information [Line Items]          
Revenues 3,382,195 1,661,129 6,563,748 3,342,274  
Cost of revenue 3,135,211 1,564,414 6,089,312 3,154,603  
Gross profit 246,984 96,715 474,436 187,671  
Total assets 7,242,286 1,364,523 7,242,286 1,364,523  
H C I T
         
Segment Reporting Information [Line Items]          
Revenues 35,235 41,574 73,399 77,526  
Cost of revenue 17,630 15,785 34,873 32,304  
Gross profit 17,605 25,789 38,526 45,222  
Total assets $ 105,526 $ 486,708 $ 105,526 $ 486,708