Stock-Based Compensation (Summary of Liability-Classified Restricted Stock Unit Activity) (Details) - Restricted Stock Units (RSUs) [Member]	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares/Units, Unvested shares/units at December 31, 2017
Number of Shares/Units, Granted	12,216,000
Number of Shares/Units, Vested	(232,000)
Number of Shares/Units, Forfeited	(2,297,000)
Number of Shares/Units, Unvested shares/units at September 30, 2018	9,687,000
Weighted Average Fair Value, Unvested shares/units at December 31, 2017 | $ / shares
Weighted Average Fair Value, Granted | $ / shares	3.69
Weighted Average Fair Value, Vested | $ / shares	5.14
Weighted Average Fair Value, Forfeited | $ / shares	5.14
Weighted Average Fair Value, Unvested shares/units at September 30, 2018 | $ / shares	$ 5.11
Workforce Reduction [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares/Units, Forfeited	(1,503,470)