Stock-Based Compensation and Employee Benefit Plans (Summary of Option Activity) (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Number of Options
Beginning balance (in shares) | shares	7,918,853
Granted (in shares) | shares	595,861
Exercised (in shares) | shares	(205,768)
Forfeited (in shares) | shares	(5,853)
Expired (in shares) | shares	(68,404)
Ending balance (in shares) | shares	8,234,689
Exercisable, number of options (in shares) | shares	6,121,753
Vested or expected to vest, number of options (in shares) | shares	8,119,911
Weighted- Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 5.75
Granted (in dollars per share) | $ / shares	5.19
Exercised (in dollars per share) | $ / shares	0.45
Forfeited (in dollars per share) | $ / shares	13.08
Expired (in dollars per share) | $ / shares	12.15
Ending balance (in dollars per share) | $ / shares	5.79
Exercisable, weighted-average exercise price (in dollars per share) | $ / shares	5.42
Vested or expected to vest, weighted-average exercise price (in dollars per share) | $ / shares	$ 5.79
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, weighted-average remaining contractual term	6 years 6 months
Outstanding, aggregate intrinsic value | $	$ 16,370
Exercisable, weighted-average remaining contractual term	5 years 9 months 18 days
Exercisable, aggregate intrinsic value | $	$ 15,507
Vested or expected to vest, weighted-average remaining contractual term	6 years 6 months
Vested or expected to vest, aggregate intrinsic value | $	$ 16,329