Stock-Based Compensation and Employee Benefit Plans (Summary of Option Activity) (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Number of Options
Beginning balance (in shares) | shares	7,918,853
Granted (in shares) | shares	1,171,180
Exercised (in shares) | shares	(559,664)
Forfeited (in shares) | shares	(375,187)
Expired (in shares) | shares	(222,400)
Ending balance (in shares) | shares	7,932,782
Exercisable, number of options (in shares) | shares	6,418,213
Vested or expected to vest, number of options (in shares) | shares	7,847,599
Weighted- Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 5.75
Granted (in dollars per share) | $ / shares	5.69
Exercised (in dollars per share) | $ / shares	0.96
Forfeited (in dollars per share) | $ / shares	7.37
Expired (in dollars per share) | $ / shares	10.80
Ending balance (in dollars per share) | $ / shares	5.86
Exercisable, weighted-average exercise price (in dollars per share) | $ / shares	5.82
Vested or expected to vest, weighted-average exercise price (in dollars per share) | $ / shares	$ 5.86
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, weighted-average remaining contractual term	5 years 4 months 23 days
Outstanding, aggregate intrinsic value | $	$ 16,097
Exercisable, weighted-average remaining contractual term	4 years 8 months 12 days
Exercisable, aggregate intrinsic value | $	$ 15,467
Vested or expected to vest, weighted-average remaining contractual term	5 years 4 months 23 days
Vested or expected to vest, aggregate intrinsic value | $	$ 16,057