Share-Based Compensation - Summary of Stock Option Activity (Details) shares in Thousands	6 Months Ended
	Jun. 30, 2019 $ / shares shares
Number of Shares Underlying Options
Outstanding at beginning of year (in shares) | shares	5,903
Granted (in shares) | shares	137
Forfeited (in shares) | shares	(261)
Expired (in shares) | shares	(89)
Outstanding at end of year (in shares) | shares	5,690
Vested and exercisable, June 30, 2019 (in shares) | shares	2,850
Vested and expected to vest, June 30. 2019 (in shares) | shares	5,463
Weighted Average Exercise Price
Outstanding at beginning of year (in dollars per share) | $ / shares	$ 13.72
Granted (in dollars per share) | $ / shares	1.35
Forfeited (in dollars per share) | $ / shares	26.18
Expired (in dollars per share) | $ / shares	12.72
Outstanding at end of year (in dollars per share) | $ / shares	12.89
Vested and exercisable, June 30, 2019 (in dollars per share) | $ / shares	21.83
Vested and expected to vest, June 30. 2019 (in dollars per share) | $ / shares	$ 13.26