Stock-Based Compensation (Summary of Option Activity) (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Number of Options
Beginning balance (in shares) | shares	11,426,296
Granted (in shares) | shares	0
Exercised (in shares) | shares	(600,209)
Forfeited (in shares) | shares	(577,946)
Expired (in shares) | shares	(191,389)
Ending balance (in shares) | shares	10,056,752
Exercisable, number of options (in shares) | shares	6,569,100
Vested or expected to vest, number of options (in shares) | shares	9,902,035
Weighted- Average Exercise Price
Beginning balance, weighted-average exercise price (in dollars per share) | $ / shares	$ 6.10
Granted (in dollars per share) | $ / shares	0.00
Exercised (in dollars per share) | $ / shares	1.16
Forfeited (in dollars per share) | $ / shares	8.76
Expired (in dollars per share) | $ / shares	12.09
Ending balance, weighted-average exercise price (in dollars per share) | $ / shares	6.13
Exercisable, weighted-average exercise price (in dollars per share) | $ / shares	5.06
Vested or expected to vest, weighted-average exercise price (in dollars per share) | $ / shares	$ 6.10
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, weighted-average remaining contractual term	7 years 1 month 7 days
Outstanding, aggregate intrinsic value | $	$ 18,611
Exercisable, weighted-average remaining contractual term	6 years 5 months 7 days
Exercisable, aggregate intrinsic value | $	$ 17,224
Vested or expected to vest, weighted-average remaining contractual term	7 years 1 month 7 days
Vested or expected to vest, aggregate intrinsic value | $	$ 18,597