Stockholders' Equity - Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Number of Options
Options outstanding at the beginning of the period (in shares)	3,950
Options Granted (in shares)	84
Options Exercised (in shares)	0
Options Cancelled (in shares)	(76)
Options outstanding at the end of the period (in shares)	3,958
Vested or expected to vest (in shares)	1,287
Exercisable (in shares)	1,287
Weighted-Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 21.54
Options Granted (in dollars per share)	8.15
Options Exercised (in dollars per share)	0.00
Options Cancelled (in dollars per share)	29.17
Balance at the end of the period (in dollars per share)	21.11
Vested or expected to vest (in dollars per share)	32.35
Exercisable (in dollars per share)	$ 32.35
Weighted-Average Remaining Contractual Term
Outstanding	5 years 3 months
Vested or expected to vest	3 years 6 months 4 days
Exercisable	3 years 6 months 4 days
Aggregate Intrinsic Value
Outstanding	$ 971
Vested or expected to vest	0
Exercisable	0
Additional disclosures related to stock options
Total intrinsic value for stock options exercised	$ 0	$ 997