Commitments Under Operating Leases (Details)
ft² in Thousands, $ in Thousands
 1 Months Ended 12 Months Ended
Jun. 24, 2015
ft²
May. 01, 2012
ft²
Mar. 16, 2010
ft²
Feb. 09, 2010
ft²
Aug. 01, 2006
ft²
Nov. 30, 2014
ft²
Jan. 31, 2013
ft²
Dec. 31, 2015
USD ($)
Integer
numberOfAgreements
numberOfBuildings
numberOfFloors
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Jun. 30, 2015
USD ($)
Jan. 31, 2012
ft²
Operating Leased Assets [Line Items]                        
Rent expense               $ 51,909 $ 51,270 $ 51,770    
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]                        
2016               42,851        
2017               37,000        
2018               25,352        
2019               20,994        
2020               16,178        
2021 and Thereafter               25,510        
Office space                        
Operating Leased Assets [Line Items]                        
Rent expense               44,577 43,277 43,715    
Office space | London, England                        
Operating Leased Assets [Line Items]                        
Term of lease 10 years                      
Area of real estate property (square feet) | ft² 16                      
Future minimum payments due               15,000        
Office space | Jacksonville, FL                        
Operating Leased Assets [Line Items]                        
Term of lease           7 years 5 months            
Area of real estate property (square feet) | ft²           50            
Future minimum payments due               4,806        
Office space | Berkeley Heights, New Jersey                        
Operating Leased Assets [Line Items]                        
Term of lease             10 years          
Area of real estate property (square feet) | ft²             24          
Future minimum payments due               5,379        
Office space | Seattle, Washington                        
Operating Leased Assets [Line Items]                        
Term of lease   10 years                    
Area of real estate property (square feet) | ft²   45                    
Future minimum payments due                     $ 8,649  
Office space | Lake Success, New York                        
Operating Leased Assets [Line Items]                        
Term of lease     11 years                  
Area of real estate property (square feet) | ft²     44                 67
Future minimum payments due               12,017        
Office space | Sunrise, Florida                        
Operating Leased Assets [Line Items]                        
Term of lease       10 years                
Area of real estate property (square feet) | ft²       64                
Future minimum payments due               5,756        
Office space | Atlanta, Georgia                        
Operating Leased Assets [Line Items]                        
Term of lease         11 years              
Area of real estate property (square feet) | ft²         160              
Future minimum payments due               8,175        
Office space | Plantation, Florida                        
Operating Leased Assets [Line Items]                        
Future minimum payments due               $ 26,644        
Number of leased buildings in Plantation, FL | Integer               2        
Future Minimum Sublease Rentals, Operating Leases, Fiscal Year Maturity [Abstract]                        
2016               $ 3,460        
2017               3,532        
2018               3,608        
2019               3,684        
2020               3,761        
2021               3,841        
Total minimum sublease payments to be received               $ 21,886        
Sublease agreements (number of agreements) | numberOfAgreements               1        
Floors in sublease agreement (number of floors) | numberOfFloors               3        
Floors in building (number of floors) | numberOfFloors               4        
Buildings with sublease on three of four floors (number of buildings) | numberOfBuildings               1        
Automobiles                        
Operating Leased Assets [Line Items]                        
Rent expense               $ 7,319 7,615 7,711    
Computers and equipment                        
Operating Leased Assets [Line Items]                        
Rent expense               $ 13 $ 378 $ 344    
Minimum | Office space | Plantation, Florida                        
Future Minimum Sublease Rentals, Operating Leases, Fiscal Year Maturity [Abstract]                        
Floors subject to surrender option (number of floors) | numberOfFloors               1        
Maximum | Office space | Plantation, Florida                        
Future Minimum Sublease Rentals, Operating Leases, Fiscal Year Maturity [Abstract]                        
Floors subject to surrender option (number of floors) | numberOfFloors               2