Stockholders' Equity (Summary of Options by Range of Exercise Prices) (Details) shares in Thousands	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, Number of shares outstanding (in shares) | shares	6,483
Options outstanding, Weighted-average remaining contractual life	6 years 10 months 28 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 12.07
Options exercisable, Number of shares (in shares) | shares	3,250
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 11.00
$1.79 - $7.60
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, minimum (in dollars per share)	1.79
Exercise price range, maximum (in dollars per share)	$ 7.33
Options outstanding, Number of shares outstanding (in shares) | shares	1,152
Options outstanding, Weighted-average remaining contractual life	6 years 5 months 19 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 6.92
Options exercisable, Number of shares (in shares) | shares	583
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 6.43
$7.95 - $9.55
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, minimum (in dollars per share)	7.45
Exercise price range, maximum (in dollars per share)	$ 7.60
Options outstanding, Number of shares outstanding (in shares) | shares	664
Options outstanding, Weighted-average remaining contractual life	6 years 4 months 6 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 9.21
Options exercisable, Number of shares (in shares) | shares	479
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 9.21
$9.90 - $10.13
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, minimum (in dollars per share)	7.95
Exercise price range, maximum (in dollars per share)	$ 9.55
Options outstanding, Number of shares outstanding (in shares) | shares	659
Options outstanding, Weighted-average remaining contractual life	5 years 8 months 19 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 10.09
Options exercisable, Number of shares (in shares) | shares	655
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 10.09
$10.31 - $11.96
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, minimum (in dollars per share)	9.90
Exercise price range, maximum (in dollars per share)	$ 10.13
Options outstanding, Number of shares outstanding (in shares) | shares	674
Options outstanding, Weighted-average remaining contractual life	7 years 22 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 11.27
Options exercisable, Number of shares (in shares) | shares	395
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 11.01
$12.09 - $12.32
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, minimum (in dollars per share)	10.31
Exercise price range, maximum (in dollars per share)	$ 11.95
Options outstanding, Number of shares outstanding (in shares) | shares	41
Options outstanding, Weighted-average remaining contractual life	2 years 10 months 6 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 12.29
Options exercisable, Number of shares (in shares) | shares	41
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 12.29
$12.45 - $12.45
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, minimum (in dollars per share)	11.96
Exercise price range, maximum (in dollars per share)	$ 12.32
Options outstanding, Number of shares outstanding (in shares) | shares	930
Options outstanding, Weighted-average remaining contractual life	9 years 4 months 17 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 12.45
Options exercisable, Number of shares (in shares) | shares	0
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 0.00
$12.46 - $13.59
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, minimum (in dollars per share)	12.45
Exercise price range, maximum (in dollars per share)	$ 12.45
Options outstanding, Number of shares outstanding (in shares) | shares	759
Options outstanding, Weighted-average remaining contractual life	3 years 9 months 4 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 13.28
Options exercisable, Number of shares (in shares) | shares	702
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 13.26
$14.30- $15.96
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, minimum (in dollars per share)	12.46
Exercise price range, maximum (in dollars per share)	$ 13.37
Options outstanding, Number of shares outstanding (in shares) | shares	697
Options outstanding, Weighted-average remaining contractual life	8 years 8 months 19 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 14.72
Options exercisable, Number of shares (in shares) | shares	61
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 15.94
$16.05 - $21.75
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, minimum (in dollars per share)	13.59
Exercise price range, maximum (in dollars per share)	$ 15.55
Options outstanding, Number of shares outstanding (in shares) | shares	721
Options outstanding, Weighted-average remaining contractual life	6 years 11 months 1 day
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 18.09
Options exercisable, Number of shares (in shares) | shares	334
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 17.44
$22.35 - $27.25
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, minimum (in dollars per share)	15.66
Exercise price range, maximum (in dollars per share)	$ 18.24
Options outstanding, Number of shares outstanding (in shares) | shares	186
Options outstanding, Weighted-average remaining contractual life	9 years 9 months 26 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 23.84
Options exercisable, Number of shares (in shares) | shares	0
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 0.00