Stock Option and Compensation Plans - Summary of Stock Option Activity (Details) shares in Thousands	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Common Stock Options
Outstanding, beginning of period (in shares) | shares	3,359
Granted (in shares) | shares	1,231
Exercised (in shares) | shares	(20)
Expired or forfeited (in shares) | shares	(765)
Outstanding, end of period (in shares) | shares	3,805
Weighted Average Exercise Price
Outstanding, beginning of period (in dollars per share) | $ / shares	$ 39.92
Granted (in dollars per share) | $ / shares	4.33
Exercised (in dollars per share) | $ / shares	1.64
Expired or forfeited (in dollars per share) | $ / shares	41.96
Outstanding, end of period (in dollars per share) | $ / shares	$ 28.18
Options exercisable at end of period (in shares) | shares	1,831
Weighted average grant date fair value (per share) of options granted during the period (in dollars per share) | $ / shares	$ 3.00