Stock-Based Compensation - Activity of stock incentive plans for options (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares
Option Shares Outstanding
Forfeited (in shares)	(70,068)
Stock Incentive Plan | Stock Options
Option Shares Outstanding
Beginning balance outstanding (in shares)	1,581,699
Granted (in shares)	15,000
Exercise of stock options (in shares)	(185,328)
Forfeited (in shares)	(3,538)
Ending balance outstanding (in shares)	1,407,833
Exercisable (in shares)	644,033
Weighted Average Exercise Price
Beginning balance outstanding (in usd per share) | $ / shares	$ 40.77
Granted (in usd per share) | $ / shares	59.55
Exercise of stock options (in usd per share) | $ / shares	23.64
Forfeited (in usd per share) | $ / shares	27.43
Ending balance outstanding (in usd per share) | $ / shares	43.25
Exercisable (in usd per share) | $ / shares	$ 39.28
Weighted average remaining life outstanding (in years)	6 years 11 months 26 days
Weighted average remaining life exercisable (in years)	6 years 6 months
Aggregate intrinsic value outstanding | $	$ 32,829
Aggregate intrinsic value exercisable | $	$ 17,577