Stockholders' Equity (Summary of Options by Range of Exercise Prices) (Details) shares in Thousands	6 Months Ended
	Jun. 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	7,177
Options outstanding, Weighted-average remaining contractual life	7 years 10 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 11.58
Options exercisable, Number of shares (in shares) | shares	3,658
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 11.04
$1.79 - $7.45
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	708
Options outstanding, Weighted-average remaining contractual life	5 years 3 months 2 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 6.33
Options exercisable, Number of shares (in shares) | shares	485
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 6.01
$7.60 - $7.60
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	748
Options outstanding, Weighted-average remaining contractual life	8 years 4 months 20 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 7.60
Options exercisable, Number of shares (in shares) | shares	214
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 7.60
$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)	7.95
Exercise price range, maximum (in dollars per share)	$ 9.55
Options outstanding, Number of shares outstanding (in shares) | shares	830
Options outstanding, Weighted-average remaining contractual life	6 years 7 months 4 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 9.20
Options exercisable, Number of shares (in shares) | shares	583
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)	9.90
Exercise price range, maximum (in dollars per share)	$ 10.13
Options outstanding, Number of shares outstanding (in shares) | shares	727
Options outstanding, Weighted-average remaining contractual life	6 years 10 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 10.09
Options exercisable, Number of shares (in shares) | shares	650
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 10.09
$10.31 - $11.95
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	726
Options outstanding, Weighted-average remaining contractual life	7 years 6 months
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 11.23
Options exercisable, Number of shares (in shares) | shares	377
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 10.84
$11.96 - $12.32
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	87
Options outstanding, Weighted-average remaining contractual life	3 years 13 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 12.12
Options exercisable, Number of shares (in shares) | shares	88
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 12.12
$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)	12.45
Exercise price range, maximum (in dollars per share)	$ 12.45
Options outstanding, Number of shares outstanding (in shares) | shares	930
Options outstanding, Weighted-average remaining contractual life	9 years 7 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)	12.46
Exercise price range, maximum (in dollars per share)	$ 13.37
Options outstanding, Number of shares outstanding (in shares) | shares	810
Options outstanding, Weighted-average remaining contractual life	4 years 25 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 13.28
Options exercisable, Number of shares (in shares) | shares	747
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 13.26
$14.30- $15.85
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	726
Options outstanding, Weighted-average remaining contractual life	9 years 3 months 30 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 14.60
Options exercisable, Number of shares (in shares) | shares	16
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 15.77
$15.96 - $21.75
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	885
Options outstanding, Weighted-average remaining contractual life	6 years 7 months 5 days
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 17.87
Options exercisable, Number of shares (in shares) | shares	498
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 17.27