Stock-Based Compensation (Summary of Liability-Classified Restricted Stock Unit Activity) (Details) - RSUs shares in Thousands	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Number of Units
Beginning balance (in shares) | shares	12,992
Granted (in shares) | shares	6,172
Vested (in shares) | shares	(3,852)
Forfeited (in shares) | shares	(1,464)
Ending balance (in shares) | shares	13,848
Weighted Average Fair Value
Beginning balance (in dollars per share) | $ / shares	$ 2.42
Granted (in dollars per share) | $ / shares	1.41
Vested (in dollars per share) | $ / shares	1.38
Forfeited (in dollars per share) | $ / shares	1.67
Ending balance (in dollars per share) | $ / shares	$ 1.69