v3.8.0.1
Summary of significant accounting policies - Adoption of ASC 606 (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Jan. 01, 2018
Dec. 31, 2017
Adoption of ASC 606        
Accumulated deficit $ (131,939)     $ (131,967)
Accounts receivable, net 28,861   $ 25,079 26,148
Prepaid expenses and other current assets 6,482   6,539 6,369
Other assets 7,577   7,903 10,082
Deferred revenue, current 76,340   75,884 61,708
Deferred revenue, net of current portion 125,174   128,588 149,168
Non-controlling interests 1,734     1,212
Revenue 58,159 $ 44,333    
Income tax expense 128 199    
Non-controlling interests 456 $ 107    
Adjustment for adoption        
Adoption of ASC 606        
Accounts receivable, net     (1,069)  
Prepaid expenses and other current assets     170  
Other assets     (2,179)  
Deferred revenue, current     14,176  
Deferred revenue, net of current portion     (20,580)  
ASC 606 | As per ASC 605        
Adoption of ASC 606        
Accounts receivable, net 29,286     26,148
Prepaid expenses and other current assets 6,567     6,369
Other assets 9,910     10,082
Deferred revenue, current 67,423     61,708
Deferred revenue, net of current portion 144,652     $ 149,168
Non-controlling interests 370      
Revenue 53,890      
Income tax expense 251      
Non-controlling interests (839)      
ASC 606 | Adjustment for adoption        
Adoption of ASC 606        
Accumulated deficit     3,257  
Accounts receivable, net (425)      
Prepaid expenses and other current assets (85)      
Other assets (2,333)      
Deferred revenue, current 8,917      
Deferred revenue, net of current portion (19,478)      
Non-controlling interests 1,364   $ 69  
Revenue 4,269      
Income tax expense (123)      
Non-controlling interests $ 1,295