Stock-based Compensation - Activity of stock incentive plans for options (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) $ / shares shares
Options Shares Outstanding
Granted (in shares)	0
Forfeited (in shares)	0
Stock Incentive Plan | Stock Options
Options Shares Outstanding
Beginning Balance Outstanding (in shares)	1,581,699
Granted (in shares)	0
Exercise of stock options (in shares)	(32,623)
Forfeited (in shares)	(2,938)
Ending Balance Outstanding (in shares)	1,546,138
Exercisable (in shares)	597,788
Weighted-Average Exercise Price
Beginning Balance Outstanding (in usd per share) | $ / shares	$ 40.77
Granted (in usd per share) | $ / shares	0.00
Exercise of stock options (in usd per share) | $ / shares	21.41
Forfeited (in usd per share) | $ / shares	25.44
Ending Balance Outstanding (in usd per share) | $ / shares	41.20
Exercisable (in usd per share) | $ / shares	$ 33.14
Weighted Average Remaining Life (Years) Outstanding	7 years 2 months 12 days
Weighted Average Remaining Life (Years) Exercisable	6 years 1 month 6 days
Aggregate Intrinsic Value Outstanding | $	$ 28,445
Aggregate Intrinsic Value Exercisable | $	$ 15,816