Stock-Based Compensation - Equity Incentive Plans (Details) - shares		12 Months Ended
	Jul. 26, 2003	Dec. 31, 2019	Dec. 31, 2018
Class of Stock
Common stock, shares reserved for future issuance		25,066,074
Common stock options outstanding		4,220,417	3,304,531
Options outstanding under earlier plans		366,974
Grant of inducement stock option		393,750
2013 Stock Incentive Plan
Class of Stock
Common shares available for grant	5,653,057	2,301,240
Maximum number of additional common shares	868,372
Common stock options outstanding		3,459,693
Restricted stock units outstanding		193,625