Interim Financial Statements - Schedule of Balance Sheet Data (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories	$ 1,039,679	$ 726,138
Deferred tax assets	562,818	506,291
Total assets	10,805,613	8,764,286
Accrued expenses and other current liabilities	781,924	637,162
Total current liabilities	1,417,230	1,135,483
Total liabilities	2,937,313	2,620,208
Retained earnings	4,433,904	2,946,733
Total stockholders' equity	7,868,300	6,144,078
Total liabilities and stockholders' equity	10,805,613	8,764,286
Balance Without Adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories	1,057,197
Deferred tax assets	547,791
Total assets	10,808,104
Accrued expenses and other current liabilities	780,749
Total current liabilities	1,277,038
Total liabilities	2,801,995
Retained earnings	4,571,713
Total stockholders' equity	8,006,109
Total liabilities and stockholders' equity	10,808,104
Adjustments | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories	17,518
Deferred tax assets	(15,027)
Total assets	2,491
Accrued expenses and other current liabilities	(1,175)
Total current liabilities	(140,192)
Total liabilities	(135,318)
Retained earnings	137,809
Total stockholders' equity	137,809
Total liabilities and stockholders' equity	2,491
Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	246,812	177,746
Deferred revenue, noncurrent	421,196	379,936
Sanofi | Balance Without Adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	186,406
Deferred revenue, noncurrent	393,118
Sanofi | Adjustments | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	(60,406)
Deferred revenue, noncurrent	(28,078)
Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	216,133	142,392
Deferred revenue, noncurrent	197,651	$ 249,263
Other | Balance Without Adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	137,522
Deferred revenue, noncurrent	230,603
Other | Adjustments | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	(78,611)
Deferred revenue, noncurrent	$ 32,952