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, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number of Shares	17,663	16,195	14,704	14,712
Options Outstanding, Weighted Average Remaining Contractual Life (in years)	6 years 9 months 29 days
Options Outstanding, Weighted Average Exercise Price	$ 3.63	$ 2.98	$ 2.62	$ 2.63
Options Outstanding, Aggregate Intrinsic Value	$ 64,122
Options Exercisable, Number of Shares	10,471
Options Exercisable, Weighted Average Exercise Price	$ 3.00
Options Exercisable, Aggregate Intrinsic Value	$ 44,598
$0.96 - $ 2.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Of Options, minimum	$ 0.96
Exercise Price Of Options, Maximum	$ 2.00
Options Outstanding, Number of Shares	2,174
Options Outstanding, Weighted Average Remaining Contractual Life (in years)	3 years 8 months 12 days
Options Outstanding, Weighted Average Exercise Price	$ 1.40
Options Outstanding, Aggregate Intrinsic Value	$ 12,751
Options Exercisable, Number of Shares	2,058
Options Exercisable, Weighted Average Exercise Price	$ 1.37
Options Exercisable, Aggregate Intrinsic Value	$ 12,116
$2.01 - $ 3.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Of Options, minimum	$ 2.01
Exercise Price Of Options, Maximum	$ 3.00
Options Outstanding, Number of Shares	3,486
Options Outstanding, Weighted Average Remaining Contractual Life (in years)	5 years 4 months 24 days
Options Outstanding, Weighted Average Exercise Price	$ 2.33
Options Outstanding, Aggregate Intrinsic Value	$ 17,184
Options Exercisable, Number of Shares	3,261
Options Exercisable, Weighted Average Exercise Price	$ 2.31
Options Exercisable, Aggregate Intrinsic Value	$ 16,141
$3.01 - $ 4.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Of Options, minimum	$ 3.01
Exercise Price Of Options, Maximum	$ 4.00
Options Outstanding, Number of Shares	6,201
Options Outstanding, Weighted Average Remaining Contractual Life (in years)	8 years 1 month 6 days
Options Outstanding, Weighted Average Exercise Price	$ 3.55
Options Outstanding, Aggregate Intrinsic Value	$ 22,991
Options Exercisable, Number of Shares	2,575
Options Exercisable, Weighted Average Exercise Price	$ 3.48
Options Exercisable, Aggregate Intrinsic Value	$ 9,745
$4.01 - $ 6.92
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Of Options, minimum	$ 4.01
Exercise Price Of Options, Maximum	$ 6.92
Options Outstanding, Number of Shares	5,802
Options Outstanding, Weighted Average Remaining Contractual Life (in years)	7 years 6 months
Options Outstanding, Weighted Average Exercise Price	$ 5.33
Options Outstanding, Aggregate Intrinsic Value	$ 11,196
Options Exercisable, Number of Shares	2,577
Options Exercisable, Weighted Average Exercise Price	$ 4.70
Options Exercisable, Aggregate Intrinsic Value	$ 6,596