Interim Financial Statements Schedule of Balance Sheet Data (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets	$ 545,077	$ 506,291
Total assets	9,951,980	8,764,286
Accrued expenses and other current liabilities	670,709	637,162
Total current liabilities	1,331,190	1,135,483
Total liabilities	2,765,554	2,620,208
Retained earnings	3,839,179	2,946,733
Total stockholders' equity	7,186,426	6,144,078
Total liabilities and stockholders' equity	9,951,980	8,764,286
Balance Without Adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets	528,784
Total assets	9,935,687
Accrued expenses and other current liabilities	669,196
Total current liabilities	1,196,875
Total liabilities	2,666,644
Retained earnings	3,921,796
Total stockholders' equity	7,269,043
Total liabilities and stockholders' equity	9,935,687
Adjustments | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets	(16,293)
Total assets	(16,293)
Accrued expenses and other current liabilities	(1,513)
Total current liabilities	(134,315)
Total liabilities	(98,910)
Retained earnings	82,617
Total stockholders' equity	82,617
Total liabilities and stockholders' equity	(16,293)
Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	308,179	177,746
Deferred revenue, noncurrent	339,040	379,936
Sanofi | Balance Without Adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	225,196
Deferred revenue, noncurrent	345,711
Sanofi | Adjustments | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	(82,983)
Deferred revenue, noncurrent	6,671
Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	180,396	142,392
Deferred revenue, noncurrent	199,401	$ 249,263
Other | Balance Without Adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	130,577
Deferred revenue, noncurrent	228,135
Other | Adjustments | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	(49,819)
Deferred revenue, noncurrent	$ 28,734