Stock-Based Compensation (Summary of Liability-Classified Restricted Stock Unit Activity) (Details) - Liability-Classified Restricted Stock Units [Member]	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares/Units, Unvested shares/units at January 1, 2018
Number of Shares/Units, Granted	12,216,000
Number of Shares/Units, Vested	(232,000)
Number of Shares/Units, Forfeited	(3,782,000)
Number of Shares/Units, Unvested shares/units at December 31, 2018	8,202,000
Weighted Average Fair Value, Unvested shares/units at January 1, 2018 | $ / shares
Weighted Average Fair Value, Granted | $ / shares	3.69
Weighted Average Fair Value, Vested | $ / shares	5.14
Weighted Average Fair Value, Forfeited | $ / shares	4.86
Weighted Average Fair Value, Unvested shares/units at December 31, 2018 | $ / shares	$ 3.41
Workforce Reduction [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares/Units, Forfeited	(2,766,610)