Net Income (Loss) Per Share (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Net loss per share - basic and diluted        
Net loss $ (42,522) $ (47,522) $ (97,169) $ (93,100)
Weighted average shares outstanding used to compute basic and diluted net loss per share 78,511 74,756 77,966 74,286
Net loss per share - basic and diluted (in usd per share) $ (0.54) $ (0.64) $ (1.25) $ (1.25)
Antidilutive shares excluded from computation of diluted net loss 11,452 13,052 11,452 13,052