Annual report pursuant to Section 13 and 15(d)

Provision for Income Taxes - Narrative (Details)

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Provision for Income Taxes - Narrative (Details) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Tax Disclosure [Abstract]      
Decrease in income tax provision $ (600,000)    
Release of valuation allowance as a result of acquisitions   $ 1,900,000  
Operating Loss Carryforwards [Line Items]      
Net deferred tax asset change 129,200,000    
Net deferred tax asset allowance change (130,000,000.0)    
Release of federal valuation allowance 1,100,000    
Increase in valuation allowance 101,500,000    
Unrecognized tax benefits 12,370,000 9,412,000 $ 6,864,000
Income tax, penalties and interest expense 0 $ 0 $ 0
Federal      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards 972,700,000    
Tax credit carryforwards 20,500,000    
Federal | Acquisitions      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards 62,400,000    
State      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards 640,200,000    
Tax credit carryforwards that do not expire 22,000,000.0    
Tax credit carryforwards that will expire beginning in 2024 6,200,000    
State | Acquisitions      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards $ 41,300,000