Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Income before income taxes			$ 2,078,511	$ 1,329,815	$ 1,225,097
Current:
Federal			560,250	786,964	686,561
State			(4,086)	8,769	28,568
Current Foreign Tax Expense (Benefit)			4,827	(1,362)	4,004
Total current tax expense			560,991	794,371	719,133
Deferred:
Federal			317,064	(377,368)	(119,849)
State			(1,258)	13,431	(3,768)
Deferred Foreign Income Tax Expense (Benefit)			3,203	3,859	(6,475)
Total deferred tax (benefit) expense			319,009	(360,078)	(130,092)
Total income tax expense (benefit)			$ 880,000	$ 434,293	$ 589,041
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
U.S. federal statutory tax rate			35.00%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent			42.30%	32.70%	48.10%
Stock-based compensation			(9.00%)	(10.90%)	(0.00%)
State and local income taxes			0.10%	1.30%	0.90%
Foreign income tax rate differential			0.70%	8.80%	12.20%
Income tax credits			(1.30%)	(1.20%)	(1.60%)
Non-deductible Branded Prescription Drug Fee			1.70%	1.90%	2.00%
Domestic production activities deduction			(2.60%)	(2.80%)	(3.20%)
Other permanent differences			2.00%	0.60%	2.80%
Deferred tax assets:
Deferred revenue			$ 102,441	$ 214,587
Deferred compensation			391,034	515,984
Fixed and intangible assets			0	21,139
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities			38,312	37,188
Other			26,387	49,100
Deferred tax assets, gross			558,174	837,998
Valuation allowance			(4,187)	(3,420)
Deferred tax assets, net			553,987	834,578
Deferred tax liabilities:
Deferred Tax Liabilities, Property, Plant and Equipment			(44,629)	0
Deferred Tax Liabilities, Other			(3,067)	(9,275)
Deferred tax liabilities, gross			(47,696)	(9,275)
Deferred Tax Assets, Net			506,291	825,303
Utilization of net operating loss carryforwards related to exercises of Nonqualified Stock Options and disqualifying dispositions of ISOs, credited to additional paid-in capital					$ 405,317
Excess Tax Benefit from Share-based Compensation, Financing Activities			0	0	405,317
Unrecognized Tax Benefits that Would Impact Effective Tax Rate			146,200	107,200	102,100
Other Comprehensive Income (Loss), Tax					24,900
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of January 1	$ 116,572	$ 146,158	117,166	116,572	57,615
Gross increases related to current year tax positions			49,028	45,575	59,909
Unrecognized Tax Benefits, Period Increase (Decrease)			(5,606)	(42,284)	(952)
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities			14,430	2,697	0
Balance as of December 31			146,158	117,166	116,572
UNITED STATES
Operating Loss Carryforwards [Line Items]
Income before income taxes			1,964,759	1,650,959	1,665,087
Foreign
Operating Loss Carryforwards [Line Items]
Income before income taxes			113,752	(321,144)	(439,990)
Accounting Standards Update 2016-09 [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred tax liabilities:
Excess Tax Benefit from Share-based Compensation, Financing Activities			191,000	$ 144,800
Additional Paid-in Capital
Deferred tax liabilities:
Utilization of net operating loss carryforwards related to exercises of Nonqualified Stock Options and disqualifying dispositions of ISOs, credited to additional paid-in capital					$ 405,317
Additional Paid-in Capital | Accounting Standards Update 2016-09 [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Deferred tax liabilities:
Excess Tax Benefit from Share-based Compensation, Financing Activities	$ 15,600
2017 Tax Cut and Jobs Act [Member]
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Remeasurement of Deferred Tax Assets due to US Tax Reform			$ 326,200
UNITED STATES
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Change in state effective rate			15.70%	0.00%	0.00%
Subsequent Event [Member] | 2017 Tax Cut and Jobs Act [Member]
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
U.S. federal statutory tax rate		21.00%