Share-Based Compensation - Summary of Stock Option Activity (Details) - Stock options shares in Thousands	6 Months Ended
	Jun. 30, 2020 $ / shares shares
Number of Shares Underlying Options
Outstanding, beginning balance (in shares) | shares	6,780
Granted (in shares) | shares	696
Exercised (in shares) | shares	(54)
Forfeited (in shares) | shares	(260)
Expired (in shares) | shares	(7)
Outstanding, ending balance (in shares) | shares	7,155
Vested and exercisable, June 30. 2020 (in shares) | shares	3,720
Vested and expected to vest, June 30. 2020 (in shares) | shares	6,845
Weighted Average Exercise Price
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 10.89
Granted (in dollars per share) | $ / shares	3.87
Exercised (in dollars per share) | $ / shares	2.65
Forfeited (in dollars per share) | $ / shares	15.59
Expired (in dollars per share) | $ / shares	1.59
Outstanding, ending balance (in dollars per share) | $ / shares	10.11
Vested and exercisable, June 30. 2020 (in dollars per share) | $ / shares	16.19
Vested and expected to vest, June 30. 2020 (in dollars per share) | $ / shares	$ 10.41