Annual report pursuant to Section 13 and 15(d)

Property and Equipment (Details)

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Property and Equipment (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Property and equipment, cost:      
Property and equipment, gross $ 89,546 $ 78,485  
Less accumulated depreciation and amortization (53,637) (45,485)  
Property and equipment, net 35,909 33,000  
Cost written off 7,712 8,123  
Accumulated depreciation written off (7,636) (7,725)  
Increase in cost of acquired property and equipment   3,922  
Depreciation and amortization expense $ 15,383 14,838 $ 7,668
Computer equipment and software      
Property and equipment, cost:      
Estimated Useful Life 3 years    
Property and equipment, gross $ 56,192 52,921  
Cost written off 7,528 6,593  
Accumulated depreciation written off (7,523) (6,498)  
Office furniture and fixtures      
Property and equipment, cost:      
Property and equipment, gross 8,110 6,911  
Cost written off 184 225  
Accumulated depreciation written off $ (113) (206)  
Office furniture and fixtures | Minimum      
Property and equipment, cost:      
Estimated Useful Life 3 years    
Office furniture and fixtures | Maximum      
Property and equipment, cost:      
Estimated Useful Life 7 years    
Leasehold improvements      
Property and equipment, cost:      
Property and equipment, gross $ 23,192 17,286  
Cost written off   130  
Accumulated depreciation written off   (105)  
Other office equipment      
Property and equipment, cost:      
Property and equipment, gross $ 2,052 1,367  
Cost written off   1,175  
Accumulated depreciation written off   $ (916)  
Other office equipment | Minimum      
Property and equipment, cost:      
Estimated Useful Life 3 years    
Other office equipment | Maximum      
Property and equipment, cost:      
Estimated Useful Life 5 years