Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2011	Feb. 16, 2012	Jun. 30, 2011
Entity Information [Line Items]
Entity Registrant Name	BERKLEY W R CORP
Entity Central Index Key	0000011544
Document Type	10-K
Document Period End Date	Dec. 31, 2011
Amendment Flag	false
Entity Common Stock, Shares Outstanding		137,880,895
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 3,736,987,598