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Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Adoption of ASU 2016-09 (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Jan. 01, 2017
Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Cumulative adjustment to accumulated deficit upon adoption of ASU 2016-09 $ 98,000    
Excess tax benefit amount booked to income tax provision 5,300,000    
Income taxes payable, non-current $ 0   $ 98,000
Accounting Standards Update 2016-09      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Cumulative adjustment to accumulated deficit upon adoption of ASU 2016-09   $ 98,000  
Income taxes payable, non-current   $ (98,000)