Stock-Based Compensation, Information about Stock Options Outstanding (Details) - Stock Options [Member]	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Information about Stock Options Outstanding [Abstract]
Options outstanding, number outstanding (in shares) | shares	5,998,837
Options outstanding, weighted average remaining contractual life	6 years 1 month 28 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.72
Options vested and exercisable, number exercisable (in shares) | shares	3,855,119
Options vested and exercisable, weighted average remaining contractual life	4 years 8 months 26 days
Options vested and exercisable, weighted average exercise price (in dollars per share)	$ 9.87
$0.24 - 1.58 [Member]
Information about Stock Options Outstanding [Abstract]
Exercise price range, lower range limit (in dollars per share)	0.24
Exercise price range, upper range limit (in dollars per share)	$ 1.58
Options outstanding, number outstanding (in shares) | shares	653,816
Options outstanding, weighted average remaining contractual life	3 months 4 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 1.16
Options vested and exercisable, number exercisable (in shares) | shares	653,816
Options vested and exercisable, weighted average remaining contractual life	3 months 4 days
Options vested and exercisable, weighted average exercise price (in dollars per share)	$ 1.16
$1.74 - 6.95 [Member]
Information about Stock Options Outstanding [Abstract]
Exercise price range, lower range limit (in dollars per share)	1.74
Exercise price range, upper range limit (in dollars per share)	$ 6.95
Options outstanding, number outstanding (in shares) | shares	4,091,396
Options outstanding, weighted average remaining contractual life	7 years 10 months 10 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 4.04
Options vested and exercisable, number exercisable (in shares) | shares	1,947,678
Options vested and exercisable, weighted average remaining contractual life	6 years 10 months 24 days
Options vested and exercisable, weighted average exercise price (in dollars per share)	$ 4.24
$14.52 - 35.25 [Member]
Information about Stock Options Outstanding [Abstract]
Exercise price range, lower range limit (in dollars per share)	14.52
Exercise price range, upper range limit (in dollars per share)	$ 35.25
Options outstanding, number outstanding (in shares) | shares	1,253,625
Options outstanding, weighted average remaining contractual life	3 years 8 months 16 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 23.16
Options vested and exercisable, number exercisable (in shares) | shares	1,253,625
Options vested and exercisable, weighted average remaining contractual life	3 years 8 months 16 days
Options vested and exercisable, weighted average exercise price (in dollars per share)	$ 23.16