Stockholders' Equity - Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) [Member] shares in Thousands	9 Months Ended
	Sep. 30, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested balance—December 31, 2016 (in shares) | shares	11,578
Granted (in shares) | shares	14,499
Vested (in shares) | shares	(4,673)
Forfeited or canceled (in shares) | shares	(3,909)
Unvested balance—September 30, 2017 (in shares) | shares	17,495
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Unvested balance—December 31, 2016 (in dollars per share) | $ / shares	$ 16.85
Granted (in dollars per share) | $ / shares	6.55
Vested (in dollars per share) | $ / shares	12.81
Forfeited or canceled (in dollars per share) | $ / shares	12.94
Unvested balance—September 30, 2017 (in dollars per share) | $ / shares	$ 10.27