Stock-based Payments - Summary of Restricted Stock Units Activity (Details) - RSUs	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Number of RSUs
Outstanding, Beginning Balance (in shares) | shares	1,028,881,000
Granted (in shares) | shares	218,500,000
Vested (in shares) | shares	(150,556,000)
Forfeited/cancelled (in shares) | shares	(651,808,000)
Outstanding, Ending Balance (in shares) | shares	445,017,000
Weighted-Average Grant Date Fair Value
Outstanding, Beginning Balance (in dollars per share) | $ / shares	$ 8.82
Granted, weighted-average fair value (in dollars per share) | $ / shares	4.59
Vested, weighted-average fair value (in dollars per share) | $ / shares	11.54
Forfeited/cancelled, weighted-average fair value (in dollars per share) | $ / shares	9.21
Outstanding, Ending Balance (in dollars per share) | $ / shares	$ 8.29