Stock-based Compensation - Stock Option (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 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		1,728,112
Shares available for future issuance			1,085,220
Shares
Outstanding at the beginning of the year (in shares)	1,461,987
Options granted (in shares)	266,125
Outstanding at the end of the year (in shares)	1,728,112
Exercisable at the end of the year (in shares)			1,025,465
Weighted average exercise price
Outstanding at the beginning of the year (in dollars per share)	$ 64.67
Options granted (in dollars per share)	90.75
Outstanding at the end of the year (in dollars per share)	$ 68.69
Exercisable at the end of the year (in dollars per share)			$ 45.81
Additional disclosures
Proceeds resulting from exercise of stock options	$ 0.0	$ 0.1
Weighted-average grant date fair value of options (in dollars per share)	$ 68.71	$ 101.08