Stock-Based Compensation and Employee Benefit Plans (Summary of Option Activity) (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Number of Options
Beginning balance (in shares) | shares	11,426,296
Granted (in shares) | shares	368,894
Exercised (in shares) | shares	(1,407,646)
Forfeited (in shares) | shares	(1,310,438)
Expired (in shares) | shares	(1,158,253)
Ending balance (in shares) | shares	7,918,853
Exercisable, number of options (in shares) | shares	6,080,899
Vested or expected to vest, number of options (in shares) | shares	7,876,541
Weighted- Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 6.10
Granted (in dollars per share) | $ / shares	4.13
Exercised (in dollars per share) | $ / shares	0.85
Forfeited (in dollars per share) | $ / shares	8.55
Expired (in dollars per share) | $ / shares	11.45
Ending balance (in dollars per share) | $ / shares	5.75
Exercisable, weighted-average exercise price (in dollars per share) | $ / shares	5.16
Vested or expected to vest, weighted-average exercise price (in dollars per share) | $ / shares	$ 5.75
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, weighted-average remaining contractual term	6 years 4 months 21 days
Outstanding, aggregate intrinsic value | $	$ 17,792
Exercisable, weighted-average remaining contractual term	5 years 10 months 2 days
Exercisable, aggregate intrinsic value | $	$ 16,989
Vested or expected to vest, weighted-average remaining contractual term	6 years 4 months 21 days
Vested or expected to vest, aggregate intrinsic value | $	$ 17,778