Acquisitions and Dispositions of Businesses (Details)
$ in Thousands
 1 Months Ended 12 Months Ended
Oct. 01, 2015
Dec. 01, 2014
USD ($)
Jul. 15, 2014
USD ($)
Feb. 28, 2014
USD ($)
Mar. 31, 2013
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Assets                
Goodwill           $ 95,616 $ 131,885 $ 132,777
Liabilities                
Amortization of intangible assets           10,410 7,084 7,127
Cash surrendered from sale of business           $ 0 $ 1,554 0
Minimum                
Business Acquisition [Line Items]                
Finite-lived intangible asset, useful life           2 years    
Maximum                
Business Acquisition [Line Items]                
Finite-lived intangible asset, useful life           15 years    
GAB Robins                
Business Acquisition [Line Items]                
Business acquisition, percentage of voting interests acquired   100.00%            
Payments to acquire businesses, preliminary gross   $ 71,812            
Business combination, provisional information, initial accounting incomplete, adjustment, consideration transferred           $ 2,182    
Payments to acquire businesses, gross           73,994    
Business combination, indemnification assets, amount as of acquisition date   $ 6,329            
Business combination, indemnification period   2 years            
Business acquisition, preacquisition contingency, amount of settlement           1,600    
Assets                
Cash and cash equivalents           5,735    
Accounts receivable           19,182    
Unbilled revenues, at estimated billable amounts           6,791    
Prepaid expenses and other current assets           7,443    
Property and equipment           4,083    
Goodwill           19,046    
Intangible assets           40,535    
Other noncurrent assets           1,933    
Deferred income tax assets           2,120    
Total Assets           106,868    
Liabilities                
Other current liabilities           22,801    
Noncurrent liabilities           4,580    
Total Liabilities           27,381    
Net Assets Acquired, Before Noncontrolling Interests           79,487    
Noncontrolling interests           5,493    
Net Assets Acquired, Net of Noncontrolling Interests           73,994    
Finite-lived intangible assets acquired   $ 38,210            
Amortization of intangible assets           3,394    
Revenue since acquisition date           $ 79,750    
GAB Robins | Customer relationships                
Business Acquisition [Line Items]                
Finite-lived intangible asset, useful life 14 years 18 years            
GAB Robins | Minimum | Intangible assets not including customer relationships                
Business Acquisition [Line Items]                
Finite-lived intangible asset, useful life           2 years    
GAB Robins | Maximum | Intangible assets not including customer relationships                
Business Acquisition [Line Items]                
Finite-lived intangible asset, useful life           5 years    
Buckley Scott                
Business Acquisition [Line Items]                
Business acquisition, percentage of voting interests acquired     100.00%          
Payments to acquire businesses, gross     $ 3,812          
Assets                
Cash and cash equivalents     488          
Goodwill     1,542          
Liabilities                
Business combination, recognized identifiable assets acquired and liabilities assumed, net     1,532          
Deferred income tax liabilities, noncurrent     $ 473          
Fair value assumptions, expected term     2 years          
Contingent earnout liability           $ 1,921    
Buckley Scott | Customer relationships                
Business Acquisition [Line Items]                
Finite-lived intangible asset, useful life     15 years          
Liabilities                
Finite-lived intangible assets acquired     $ 2,195          
Buckley Scott | Trade name                
Business Acquisition [Line Items]                
Finite-lived intangible asset, useful life     2 years          
Liabilities                
Finite-lived intangible assets acquired     $ 169          
Lloyd Warwick International                
Liabilities                
Variable interest entity, ownership percentage         51.00%      
Noncontrolling interest, ownership percentage by noncontrolling owners (percent)           49.00%    
Business combination, right to purchase noncontrolling interest, term           6 months    
Fair value inputs, earnings before interest, taxes, depreciation, and amortization multiple           7    
Fair value inputs, period to be used in valuation           36 months    
Business combination, right of first refusal, term           30 days    
Crawford South Africa                
Liabilities                
Sale of stock, percentage of ownership before transaction       74.90%        
Net assets sold       $ 2,542        
Cash surrendered from sale of business       $ 1,554        
Loss on disposition of business               $ 474