Stock-based Compensation Expense Fixed-Price Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Outstanding Shares,Beginning Balance (in shares)	1,401,718
Granted (in shares)	63,259	82,204	141,661
Exercised (in shares)	(94,031)
Forfeited (in shares)	(54,213)
Outstanding Shares, Ending Balance (in shares)	1,316,733	1,401,718
Exercisable, Ending Balance (in shares)	911,011
Weighted-Average Exercise Price
Outstanding Weighted-Average Exercise Price, Beginning Balance (in dollars per share)	$ 56.10
Granted (in dollars per share)	118.75
Exercised (in dollars per share)	38.64
Forfeited (in dollars per share)	75.72
Outstanding Weighted-Average Exercise (in dollars per share)Price, Ending Balance	59.55	$ 56.10
Exercisable Weighted-Average Exercise Price, Ending Balance (in dollars per share)	$ 54.28
Weighted-Average Remaining Contractual Term (Years)
Weighted-Averaged Remaining Contractual Term, Beginning Balance	4 years 4 months	5 years 1 month
Weighted-Averaged Remaining Contractual Term, Ending Balance	4 years 4 months	5 years 1 month
Exercisable Weighted-Average Remaining Contractual Term, Ending Balance	3 years 2 months 3 days
Aggregate Intrinsic Value
Outstanding Aggregate Intrinsic Value, Beginning Balance	$ 100,632
Outstanding Aggregate Intrinsic Value, Ending Balance	26,438	$ 100,632
Exercisable Aggregate Intrinsic Value, Ending Balance	$ 20,872