Segment Information (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
segment
Jun. 30, 2013
Dec. 31, 2013
Segment Reporting Information [Line Items]          
Number of operating segments     2    
Revenue $ 5,385,808 $ 3,417,430 $ 10,300,287 $ 6,637,147  
Cost of revenue 5,055,995 3,152,841 9,655,813 6,124,185  
Gross profit 329,813 264,589 644,474 512,962  
Total assets 9,117,886 7,347,812 9,117,886 7,347,812 7,995,763
P B M [Member]
          
Segment Reporting Information [Line Items]          
Revenue 5,350,962 3,382,195 10,229,337 6,563,748  
Cost of revenue 5,039,279 3,135,211 9,622,564 6,089,312  
Gross profit 311,683 246,984 606,773 474,436  
Total assets 8,744,311 7,242,286 8,744,311 7,242,286  
H C I T [Member]
          
Segment Reporting Information [Line Items]          
Revenue 34,846 35,235 70,950 73,399  
Cost of revenue 16,716 17,630 33,249 34,873  
Gross profit 18,130 17,605 37,701 38,526  
Total assets $ 373,575 $ 105,526 $ 373,575 $ 105,526