Stock-Based Compensation and Employee Benefit Plans (Summary of Option Activity) (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) $ / shares shares
Number of Options
Beginning balance (in shares) | shares	7,932,782
Exercised (in shares) | shares	(315,959)
Expired (in shares) | shares	(182,492)
Ending balance (in shares) | shares	7,434,331
Exercisable, number of options (in shares) | shares	6,207,892
Vested or expected to vest, number of options (in shares) | shares	7,372,107
Weighted- Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 5.86
Exercised (in dollars per share) | $ / shares	3.15
Expired (in dollars per share) | $ / shares	12.19
Ending balance (in dollars per share) | $ / shares	5.82
Exercisable, weighted-average exercise price (in dollars per share) | $ / shares	5.79
Vested or expected to vest, weighted-average exercise price (in dollars per share) | $ / shares	$ 5.82
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, weighted-average remaining contractual term	5 years 6 months
Outstanding, aggregate intrinsic value | $	$ 13,360
Exercisable, weighted-average remaining contractual term	4 years 10 months 24 days
Exercisable, aggregate intrinsic value | $	$ 13,165
Vested or expected to vest, weighted-average remaining contractual term	5 years 6 months
Vested or expected to vest, aggregate intrinsic value | $	$ 13,351