Stock-Based Incentive Compensation Plans - Stock Option Activity Under the Stock Option Plan (Details)	6 Months Ended
	Jun. 30, 2019 $ / shares shares
Number of Shares
Beginning balance (in shares) | shares	2,641,198
Options granted (in shares) | shares	630,639
Options exercised (in shares) | shares	(184,130)
Options cancelled (in shares) | shares	(62,964)
Ending balance (in shares) | shares	3,024,743
Weighted- Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 4.27
Options granted (in dollars per share) | $ / shares	20.91
Options exercised (in dollars per share) | $ / shares	3.10
Options cancelled (in dollars per share) | $ / shares	6.61
Ending balance (in dollars per share) | $ / shares	$ 7.76