Quarterly Financial Data (Unaudited) Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues	$ 843,968	$ 753,866	$ 731,366	$ 679,452	$ 817,923	$ 734,846	$ 721,996	$ 660,821	$ 3,008,652	$ 2,935,586	$ 2,725,053
Gross profit	498,298	435,056	419,538	388,319	477,566	419,254	412,625	374,933	1,741,211	1,684,378	1,575,751
Net earnings	$ 192,749	$ 129,395	$ 127,160	$ 111,805	$ 181,186	$ 126,653	$ 111,468	$ 93,304	$ 561,109	$ 512,611	$ 375,972
Basic earnings per common share:
Net earnings	$ 7.95	$ 5.28	$ 5.15	$ 4.50	$ 7.25	$ 5.04	$ 4.41	$ 3.66	$ 22.84	$ 20.33	$ 14.62
Weighted average number of common shares	24,241,383	24,487,268	24,698,032	24,851,340	24,975,303	25,126,061	25,299,414	25,468,323	24,567,609	25,215,674	25,713,575
Diluted earnings per common share:
Net earnings	$ 7.84	$ 5.20	$ 5.06	$ 4.42	$ 7.11	$ 4.93	$ 4.31	$ 3.58	$ 22.47	$ 19.88	$ 14.24
Weighted average number of common and common equivalent shares	24,599,702	24,880,179	25,118,352	25,310,525	25,490,270	25,683,365	25,867,383	26,095,647	24,974,457	25,781,324	26,393,783
Market price per share:
Common Stock Value During The Period Maximum	$ 793.31	$ 872.45	$ 840.00	$ 729.72	$ 645.33	$ 617.94	$ 595.14	$ 692.30
Common Stock Value During The Period Mimimum	$ 658.61	$ 642.84	$ 701.80	$ 513.56	$ 524.03	$ 559.44	$ 546.43	$ 566.87
Provisional one-time charge on US tax reform									$ 0	$ 3,597	$ 71,982
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability									$ 0	(18,674)	$ 0
Loss Contingency Accrual					$ 3,000					3,000
BIOTIX [Member]
Market price per share:
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability										$ 18,700