Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Recent Accounting Pronouncement) (Details)

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Summary of Significant Accounting Policies (Recent Accounting Pronouncement) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Retained earnings $ (73,854) $ (70,574)    
Net cash provided by (used in) operating activities $ 108,607 81,270 $ 42,035  
Accounting Standards Update 2014-09        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Revenue recognition period 5 years      
Accounting Standards Update 2014-09 | Difference between revenue guidance in effect before and after Topic 606        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Retained earnings       $ 9,000
Deferred revenue       (4,000)
Noncurrent assets       $ 5,000
Accounting Standards Update 2016-09 | Adjustments for New Accounting Principle, Early Adoption        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Net cash provided by (used in) operating activities   $ 4,455 $ 17,607