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Commitments and Contingencies - Lease Commitments (Details)
ft² in Thousands
12 Months Ended
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Jan. 31, 2018
USD ($)
ft²
Property, Plant and Equipment [Line Items]        
Operating lease rent expense $ 4,700,000 $ 3,900,000 $ 3,700,000  
Capital leased assets 37,274,000 38,350,000    
COLORADO | Subsequent event        
Property, Plant and Equipment [Line Items]        
New lease agreement, area of property (in square feet) | ft²       30
Aggregate annual payment under new lease       $ 1,000,000.0
Computer Equipment and Furniture        
Property, Plant and Equipment [Line Items]        
Capital leased assets $ 0 $ 0 $ 500,000