Preferred Stock and Stockholders' Equity (Summary of Options Outstanding and Exercisable) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Stock options outstanding (in shares)	23,600	22,826	20,454	17,663
Options Outstanding, Weighted Average Remaining Contractual Life (in years)	6 years 6 months
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 8.77	$ 7.72	$ 5.22	$ 3.63
Options Outstanding, Aggregate Intrinsic Value	$ 100,062
Options Exercisable, Number of Shares (in shares)	15,398
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.80
Options Exercisable, Aggregate Intrinsic Value	$ 91,283
$0.96 - $ 4.00
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise Price Of Options, minimum (in dollars per share)	$ 1.48
Exercise Price Of Options, maximum (in dollars per share)	$ 4.00
Stock options outstanding (in shares)	6,950
Options Outstanding, Weighted Average Remaining Contractual Life (in years)	4 years 2 months 12 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 3.02
Options Outstanding, Aggregate Intrinsic Value	$ 63,079
Options Exercisable, Number of Shares (in shares)	6,874
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 3.11
Options Exercisable, Aggregate Intrinsic Value	$ 62,446
$4.01 - $ 9.00
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise Price Of Options, minimum (in dollars per share)	$ 4.01
Exercise Price Of Options, maximum (in dollars per share)	$ 7.00
Stock options outstanding (in shares)	3,233
Options Outstanding, Weighted Average Remaining Contractual Life (in years)	4 years 3 months 18 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 5.32
Options Outstanding, Aggregate Intrinsic Value	$ 21,974
Options Exercisable, Number of Shares (in shares)	2,949
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.22
Options Exercisable, Aggregate Intrinsic Value	$ 20,296
$9.01 - $ 17.00
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise Price Of Options, minimum (in dollars per share)	$ 7.01
Exercise Price Of Options, maximum (in dollars per share)	$ 15.00
Stock options outstanding (in shares)	9,353
Options Outstanding, Weighted Average Remaining Contractual Life (in years)	8 years 3 months 18 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 10.73
Options Outstanding, Aggregate Intrinsic Value	$ 15,009
Options Exercisable, Number of Shares (in shares)	3,714
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 9.99
Options Exercisable, Aggregate Intrinsic Value	$ 8,541
$17.01 - $ 24.29
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise Price Of Options, minimum (in dollars per share)	$ 15.01
Exercise Price Of Options, maximum (in dollars per share)	$ 24.29
Stock options outstanding (in shares)	4,064
Options Outstanding, Weighted Average Remaining Contractual Life (in years)	8 years 1 month 6 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 16.85
Options Outstanding, Aggregate Intrinsic Value	$ 0
Options Exercisable, Number of Shares (in shares)	1,861
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 16.89
Options Exercisable, Aggregate Intrinsic Value	$ 0