v3.6.0.2
Stock incentive plans - Plans (Details) - shares
12 Months Ended 70 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2016
Stock options      
Stock incentive plans      
Number of stock options granted 0 0  
Number of stock options outstanding 3,084,000 3,748,000 3,084,000
RSUs      
Stock incentive plans      
Number of RSUs granted (in shares) 3,200,000    
2011 Plan      
Stock incentive plans      
Common stock shares reserved for issuance 12,004,534   12,004,534
Annual percentage increase alternative, increase in common stock reserved for issuance as a percentage of common stock outstanding 4.50%    
Annual fixed increase alternative, increase in shares of common stock reserved for issuance (in shares) 3,000,000    
Number of stock options outstanding 1,994,000 2,528,000 1,994,000
2011 Plan | Stock options      
Stock incentive plans      
Number of stock options granted     5,229,486
2011 Plan | RSUs      
Stock incentive plans      
Number of RSUs granted (in shares)     7,096,225
2001 Plan      
Stock incentive plans      
Number of stock options outstanding 1,090,000 1,220,000 1,090,000
2001 Plan | Stock options      
Stock incentive plans      
Number of stock options outstanding 1,089,702   1,089,702