Stock-Based Compensation (Summary of Option Activity) (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2016 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning Balance, Outstanding, Number of Options (in shares) | shares	10,711,324
Granted, Number of Options (in shares) | shares	2,022,999
Exercised, Number of Options (in shares) | shares	(420,846)
Forfeited, Number of Options (in shares) | shares	(234,919)
Expired, Number of Options (in shares) | shares	(81,007)
Ending Balance, Outstanding, Number of Options (in shares) | shares	11,997,551
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning Balance, Outstanding, Weighted-Average Exercise Price (USD per share) | $ / shares	$ 6.16
Granted, Weighted-Average Exercise Price (USD per share) | $ / shares	5.98
Exercised, Weighted-Average Exercise Price (USD per share) | $ / shares	0.59
Forfeited, Weighted-Average Exercise Price (USD per share) | $ / shares	9.47
Expired, Weighted-Average Exercise Price (USD per share) | $ / shares	12.59
Ending Balance, Outstanding, Weighted-Average Exercise Price (USD per share) | $ / shares	$ 6.20
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, Weighted-Average Remaining Contractual Term (in years)	7 years 6 months 26 days
Outstanding, Aggregate Intrinsic Value | $	$ 25,101
Exercisable, Number of Options (in shares) | shares	6,629,040
Exercisable, Weighted-Average Exercise Price (USD per share) | $ / shares	$ 4.51
Exercisable, Weighted-Average Remaining Contractual Term (in years)	6 years 8 months 27 days
Exercisable, Aggregate Intrinsic Value | $	$ 21,610
Vested or expected to vest, Number of Options (in shares) | shares	11,721,660
Vested or expected to vest, Weighted-Average Exercise Price (USD per share) | $ / shares	$ 6.16
Vested or expected to vest, Weighted-Average Remaining Contractual Term (in years)	7 years 6 months 26 days
Vested or expected to vest, Aggregate Intrinsic Value | $	$ 25,063