Stock-Based Compensation (Stock Options Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Vested and Expected to Vest (in shares)	1,500	11,500	31,500
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding — Beginning of period (in shares)	8,673,215
Granted (in shares)	5,370,408
Exercised (in shares)	(129,478)
Forfeited (in shares)	(1,405,534)
Expired (in shares)	(684,279)
Outstanding — End of period (in shares)	11,824,332	8,673,215
Vested and Expected to Vest (in shares)	10,629,743
Vested, Number of Stock Options (Shares)	5,041,775
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding — Beginning of period (in USD per share)	$ 9.22
Granted (in USD per share)	5.44
Exercised (in USD per share)	4.21
Forfeited (in USD per share)	8.20
Expired (in USD per share)	11.38
Outstanding — End of period (in USD per share)	7.56	$ 9.22
Vested and Expected to Vest, Weighted Average Exercise Price (USD per share)	7.67
Vested, Weighted Average Exercise Price (USD per share)	$ 8.48
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, Weighted Average Remaining Contractual Life	7 years 32 days
Vested and Expected to Vest, Weighted Average Remaining Contractual Life	6 years 9 months 51 days
Vested, Weighted Average Remaining Contractual Life	4 years 10 months 19 days
Exercised, Aggregate Intrinsic Value	$ 226	$ 2,700	$ 3,200	[1]
Outstanding, Aggregate Intrinsic Value	4,570
Vested and Expected to Vest, Aggregate Intrinsic Value	4,173
Vested, Aggregate Intrinsic Value	$ 2,530

[1] Represents the total difference between the Company's stock price at the time of exercise and the stock option exercise price, multiplied by the number of options exercised.