Goodwill and Acquired Intangible Assets - Additional Information (Details) $ in Millions	Dec. 31, 2017 USD ($)
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	$ 4.0
Finite-Lived Intangible Assets, Amortization Expense, Year Four	2.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill, Total	0.2
Finite-Lived Intangible Assets, Amortization Expense, Year Two	4.0
Finite-Lived Intangible Assets, Amortization Expense, Year Three	3.9
Finite-Lived Intangible Assets, Amortization Expense, Year Five	$ 2.2