Stockholders' Equity (Summary of Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Options
Outstanding Options, Beginning of period	12,530,297
Options granted	1,621,222
Options exercised	(8,063)
Options cancelled	(9,880)
Options expired	(6,250)
Outstanding Options, End of period	14,127,326
Exercisable at the end of period	9,409,292
Weighted-Average Exercise Price
Outstanding Exercise Price (in dollars per share)	$ 14.57
Options granted (in dollars per share)	13.93
Options exercised (in dollars per share)	11.87
Options cancelled (in dollars per share)	12.97
Options expired (in dollars per share)	25.36
Outstanding Exercise Price (in dollars per share)	14.50
Exercisable at the end of period (in dollars per share)	$ 14.99
Additional Disclosures
Outstanding Contractual Term (in Years)	4 years 7 months 21 days
Outstanding Intrinsic Value	$ 20,642
Exercisable at the end of period (in Years)	3 years 1 month 2 days
Exercisable aggregate intrinsic value	$ 14,611
Allocated share based compensation	4,451	$ 3,851
Employee Stock Option
Additional Disclosures
Allocated share based compensation	2,000	2,100
Employee Stock Option | Board of Directors
Additional Disclosures
Allocated share based compensation	$ 100	$ 200