Stock-based Compensation - Stock Option (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020
Maximum
Stock-based compensation expense
Expiration period	10 years
Stock options
Stock-based compensation expense
Options outstanding to purchase of common stock	1,461,987		1,820,142
Shares available for future issuance			984,220
Shares
Outstanding at the beginning of the year (in shares)	1,461,987
Options granted (in shares)	381,125
Options exercised (in shares)	(8,970)
Options cancelled (in shares)	(14,000)
Outstanding at the end of the year (in shares)	1,820,142
Exercisable at the end of the year (in shares)			1,123,761
Weighted average exercise price
Outstanding at the beginning of the year (in dollars per share)	$ 64.67
Options granted (in dollars per share)	88.04
Options exercised (in dollars per share)	12.19
Options cancelled (in dollars per share)	80.99
Outstanding at the end of the year (in dollars per share)	$ 69.70
Exercisable at the end of the year (in dollars per share)			$ 51.06
Additional disclosures
Proceeds resulting from exercise of stock options	$ 0.1	$ 0.2
Weighted-average grant date fair value of options (in dollars per share)	$ 64.74	$ 92.97