Stock-Based Compensation and Employee Benefit Plans (Summary of Option Activity) (Details) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares
Number of Options
Beginning balance (in shares) | shares	7,932,782
Exercised (in shares) | shares	(389,335)
Expired (in shares) | shares	(508,557)
Ending balance (in shares) | shares	7,034,890
Exercisable, number of options (in shares) | shares	6,093,122
Vested or expected to vest, number of options (in shares) | shares	6,984,662
Weighted- Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 5.86
Exercised (in dollars per share) | $ / shares	2.63
Expired (in dollars per share) | $ / shares	11.24
Ending balance (in dollars per share) | $ / shares	5.65
Exercisable, weighted-average exercise price (in dollars per share) | $ / shares	5.63
Vested or expected to vest, weighted-average exercise price (in dollars per share) | $ / shares	$ 5.65
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 | $	$ 9,043
Exercisable, weighted-average remaining contractual term	5 years 1 month 6 days
Exercisable, aggregate intrinsic value | $	$ 9,043
Vested or expected to vest, weighted-average remaining contractual term	5 years 6 months
Vested or expected to vest, aggregate intrinsic value | $	$ 9,043