Stockholders' Equity - Options Outstanding Separated Into Range of Exercise Price (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Class of Stock [Line Items]
Exercise price range, number of outstanding options | shares	709,668,000
Exercise price range, outstanding options, weighted average remaining contractual term	4 years 6 months 5 days
Exercise price range, outstanding options, weighted average exercise price	$ 17.941
Exercise price range, number of exercisable options | shares	687,508,000
Exercise price range, exercisable options, weighted average remaining contractual term	4 years 5 months 8 days
Exercise price range, exercisable options, weighted average exercise price	$ 17.856
Range One
Class of Stock [Line Items]
Exercise price range, upper range limit	1.576
Exercise price range, lower range limit	$ 1.256
Exercise price range, number of outstanding options | shares	130,479,000
Exercise price range, outstanding options, weighted average remaining contractual term	7 months 29 days
Exercise price range, outstanding options, weighted average exercise price	$ 1.282
Exercise price range, number of exercisable options | shares	130,479,000
Exercise price range, exercisable options, weighted average remaining contractual term	7 months 29 days
Exercise price range, exercisable options, weighted average exercise price	$ 1.282
Range Two
Class of Stock [Line Items]
Exercise price range, upper range limit	8.800
Exercise price range, lower range limit	$ 6.230
Exercise price range, number of outstanding options | shares	12,356,000
Exercise price range, outstanding options, weighted average remaining contractual term	3 years 3 days
Exercise price range, outstanding options, weighted average exercise price	$ 8.039
Exercise price range, number of exercisable options | shares	12,356,000
Exercise price range, exercisable options, weighted average remaining contractual term	3 years 3 days
Exercise price range, exercisable options, weighted average exercise price	$ 8.039
Range Three
Class of Stock [Line Items]
Exercise price range, upper range limit	16.870
Exercise price range, lower range limit	$ 12.470
Exercise price range, number of outstanding options | shares	147,125,000
Exercise price range, outstanding options, weighted average remaining contractual term	5 years 5 days
Exercise price range, outstanding options, weighted average exercise price	$ 14.030
Exercise price range, number of exercisable options | shares	132,541,000
Exercise price range, exercisable options, weighted average remaining contractual term	4 years 9 months 11 days
Exercise price range, exercisable options, weighted average exercise price	$ 13.637
Range Four
Class of Stock [Line Items]
Exercise price range, upper range limit	21.660
Exercise price range, lower range limit	$ 19.510
Exercise price range, number of outstanding options | shares	220,211,000
Exercise price range, outstanding options, weighted average remaining contractual term	5 years 7 months 6 days
Exercise price range, outstanding options, weighted average exercise price	$ 21.174
Exercise price range, number of exercisable options | shares	218,573,000
Exercise price range, exercisable options, weighted average remaining contractual term	5 years 7 months 4 days
Exercise price range, exercisable options, weighted average exercise price	$ 21.185
Range Five
Class of Stock [Line Items]
Exercise price range, upper range limit	24.230
Exercise price range, lower range limit	$ 22.010
Exercise price range, number of outstanding options | shares	85,870,000
Exercise price range, outstanding options, weighted average remaining contractual term	5 years 3 months 12 days
Exercise price range, outstanding options, weighted average exercise price	$ 22.364
Exercise price range, number of exercisable options | shares	85,870,000
Exercise price range, exercisable options, weighted average remaining contractual term	5 years 3 months 12 days
Exercise price range, exercisable options, weighted average exercise price	$ 22.364
Range Six
Class of Stock [Line Items]
Exercise price range, number of outstanding options | shares	66,349,000
Exercise price range, outstanding options, weighted average remaining contractual term	6 years 1 month 23 days
Exercise price range, outstanding options, weighted average exercise price	$ 29.880
Exercise price range, number of exercisable options | shares	60,411,000
Exercise price range, exercisable options, weighted average remaining contractual term	6 years 1 month 23 days
Exercise price range, exercisable options, weighted average exercise price	$ 29.880
Range Seven
Class of Stock [Line Items]
Exercise price range, number of outstanding options | shares	47,278,000
Exercise price range, outstanding options, weighted average remaining contractual term	5 years 2 months 21 days
Exercise price range, outstanding options, weighted average exercise price	$ 39.860
Exercise price range, number of exercisable options | shares	47,278,000
Exercise price range, exercisable options, weighted average remaining contractual term	5 years 2 months 21 days
Exercise price range, exercisable options, weighted average exercise price	$ 39.860