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Property and Equipment - Additional information (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Property Plant And Equipment [Line Items]      
Depreciation expense $ 18.7us-gaap_Depreciation $ 17.0us-gaap_Depreciation $ 13.0us-gaap_Depreciation
Software Development      
Property Plant And Equipment [Line Items]      
Capitalized internal software development costs $ 8.6us-gaap_CapitalizedComputerSoftwareAdditions
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_SoftwareAndSoftwareDevelopmentCostsMember
$ 6.6us-gaap_CapitalizedComputerSoftwareAdditions
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_SoftwareAndSoftwareDevelopmentCostsMember
$ 8.1us-gaap_CapitalizedComputerSoftwareAdditions
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_SoftwareAndSoftwareDevelopmentCostsMember