Cover Page - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Feb. 21, 2020	Jun. 30, 2019
Cover page.
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	0-30739
Entity Registrant Name	INSMED INC
Entity Address, Address Line One	700 US Highway 202/206
Entity Address, Address Line Two
Entity Address, City or Town	Bridgewater
Entity Incorporation, State or Country Code	VA
Entity Tax Identification Number	54-1972729
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	08807
City Area Code	908
Local Phone Number	977-9900
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	INSM
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 2.3
Entity Common Stock, Shares Outstanding		89,775,696
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0001104506
Current Fiscal Year End Date	--12-31
Documents Incorporated by Reference	Portions of the registrant's definitive Proxy Statement for its 2020 Annual Meeting of Shareholders to be filed with the Securities and Exchange Commission no later than April 29, 2020 and to be delivered to shareholders in connection with the 2020 Annual Meeting of Shareholders, are herein incorporated by reference in Part III of this Annual Report on Form 10-K