Description of Business and Summary of Significant Accounting Policies (Recent Accounting Pronouncements) (Details) - USD ($)
$ in Millions
9 Months Ended 12 Months Ended
Jan. 01, 2017
Sep. 30, 2017
Dec. 31, 2016
Accounting Standards Update 2016-09 | Adjustment      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Recognition of excess tax benefits   $ 9.6  
Increase in net valuation allowance   $ 9.6  
Accounting Standards Update 2014-09 | Maximum | Revenue Streams | Overall Revenue      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Concentration risk, percentage     5.00%
Accumulated Deficit | Accounting Standards Update 2016-09 | Adjustment      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
New accounting pronouncement, cumulative effect of change, accumulated deficit increase (decrease) $ 0.3    
State      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Unrecorded tax benefits for stock-based compensation     $ 17.6
Domestic | Accounting Standards Update 2016-09 | Adjustment      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Deferred tax assets, operating loss carryforwards 7.7    
Domestic | Accounting Standards Update 2016-09 | Valuation allowance, operating loss carryforwards | Adjustment      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Increase in net valuation allowance 7.7    
Domestic | Accumulated Deficit | Accounting Standards Update 2016-09 | Adjustment      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
New accounting pronouncement, cumulative effect of change, accumulated deficit increase (decrease) (7.7)    
Domestic | Accumulated Deficit | Accounting Standards Update 2016-09 | Valuation allowance, operating loss carryforwards | Adjustment      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
New accounting pronouncement, cumulative effect of change, accumulated deficit increase (decrease) $ 7.7    
Federal      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Unrecorded tax benefits for stock-based compensation     $ 20.6