Stock-Based Compensation and Employee Benefit Plans (Summary of Option Activity) (Details) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Number of Options
Beginning balance (in shares) | shares	7,918,853
Granted (in shares) | shares	1,031,550
Exercised (in shares) | shares	(380,151)
Forfeited (in shares) | shares	(211,743)
Expired (in shares) | shares	(93,402)
Ending balance (in shares) | shares	8,265,107
Exercisable, number of options (in shares) | shares	6,393,532
Vested or expected to vest, number of options (in shares) | shares	8,142,643
Weighted- Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 5.75
Granted (in dollars per share) | $ / shares	5.41
Exercised (in dollars per share) | $ / shares	0.55
Forfeited (in dollars per share) | $ / shares	8.16
Expired (in dollars per share) | $ / shares	11.81
Ending balance (in dollars per share) | $ / shares	5.82
Exercisable, weighted-average exercise price (in dollars per share) | $ / shares	5.62
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	6 years 1 month 6 days
Outstanding, aggregate intrinsic value | $	$ 22,721
Exercisable, weighted-average remaining contractual term	5 years 4 months 24 days
Exercisable, aggregate intrinsic value | $	$ 20,300
Vested or expected to vest, weighted-average remaining contractual term	6 years 1 month 6 days
Vested or expected to vest, aggregate intrinsic value | $	$ 22,521