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Segment Information - Additional Information (Detail) (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
Segment
Dec. 31, 2012
Dec. 31, 2011
Segment Reporting Information [Line Items]                      
Number of reportable segments                 4    
Total revenues $ 343,165 $ 359,310 $ 325,792 $ 335,012 $ 302,830 $ 303,800 $ 290,916 $ 302,486 $ 1,363,279 $ 1,200,032 $ 1,013,542
London Operation [Member]
                     
Segment Reporting Information [Line Items]                      
Total revenues                 $ 12,200 $ 9,700 $ 9,100