Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Schedule of Adjustments Due to Change in Accounting Policy (Details)

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Summary of Significant Accounting Policies - Schedule of Adjustments Due to Change in Accounting Policy (Details) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Jan. 01, 2018
Dec. 31, 2017
Dec. 31, 2016
Assets          
Accounts receivable, less allowance for doubtful accounts $ 114,441   $ 116,580 $ 124,505  
Other current assets 17,834   9,393 6,622  
Deferred tax assets, net 42,397   44,107 44,887  
Other assets 18,992   15,469 11,010  
Liabilities          
Current portion of deferred revenue 110,507   112,926 116,622  
Stockholders’ equity:          
Accumulated deficit (44,372)   (72,825) (75,046)  
Statement of Cash Flows for the nine months ended September 30, 2017          
Net cash provided by operating activities 134,962 $ 105,883      
Net cash used in investing activities (269,561) (386,126)      
Cash, cash equivalents and restricted cash at end of period 370,791 201,894   165,345 $ 188,540
Previously Reported          
Statement of Cash Flows for the nine months ended September 30, 2017          
Net cash provided by operating activities   106,288      
Net cash used in investing activities   (395,437)      
Cash, cash equivalents and restricted cash at end of period   109,334      
Adjustments due to accounting standards update 2016-18          
Statement of Cash Flows for the nine months ended September 30, 2017          
Net cash provided by operating activities   (405)      
Net cash used in investing activities   9,311      
Cash, cash equivalents and restricted cash at end of period   $ 92,560      
Balances without adoption of ASU 2014-09          
Assets          
Accounts receivable, less allowance for doubtful accounts       124,505  
Other current assets       6,622  
Deferred tax assets, net       44,887  
Other assets       11,010  
Liabilities          
Current portion of deferred revenue       116,622  
Stockholders’ equity:          
Accumulated deficit       $ (75,046)  
Balances without adoption of ASU 2014-09 | Adjustments due to ASU 2014-09          
Assets          
Accounts receivable, less allowance for doubtful accounts 121,816        
Other current assets 11,997        
Other assets 11,446        
Liabilities          
Current portion of deferred revenue 114,779        
Effect of Change on Net Income Higher/(Lower) | Adjustments due to ASU 2014-09          
Assets          
Accounts receivable, less allowance for doubtful accounts (7,375)   (7,925)    
Other current assets 5,837   2,771    
Deferred tax assets, net     (780)    
Other assets 7,546   4,459    
Liabilities          
Current portion of deferred revenue $ (4,272)   (3,696)    
Stockholders’ equity:          
Accumulated deficit     $ 2,221