Stock-Based Compensation - Activity of stock incentive plans for options (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares
Option Shares Outstanding
Forfeited (in shares)	(17,699)
Stock Incentive Plan | Stock Options
Option Shares Outstanding
Beginning balance outstanding (in shares)	1,443,733
Granted (in shares)	44,500
Exercise of stock options (in shares)	(47,237)
Forfeited (in shares)	0
Ending balance outstanding (in shares)	1,440,996
Exercisable (in shares)	747,746
Weighted Average Exercise Price
Beginning balance outstanding (in usd per share) | $ / shares	$ 48.75
Granted (in usd per share) | $ / shares	70.09
Exercise of stock options (in usd per share) | $ / shares	(23.26)
Forfeited (in usd per share) | $ / shares	0
Ending balance outstanding (in usd per share) | $ / shares	50.24
Exercisable (in usd per share) | $ / shares	$ 44.44
Weighted average remaining life outstanding (in years)	6 years 9 months 18 days
Weighted average remaining life exercisable (in years)	6 years 2 months 12 days
Aggregate intrinsic value outstanding | $	$ 10,300
Aggregate intrinsic value exercisable | $	$ 7,727