Subsequent Events (Details) (USD $)	9 Months Ended			3 Months Ended					9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Sep. 30, 2011 Kilroy Realty, L.P. [Member] 6.70% Mortgage Payable due Dec 27, 2011 [Member] Repayment of Debt [Member]	Sep. 30, 2011 Kilroy Realty, L.P. [Member] 5.10% Mortgage Payable due April 1, 2012 [Member] Repayment of Debt [Member]	Sep. 30, 2011 Dividend Paid [Member]	Sep. 30, 2011 Acquisition [Member]	Sep. 30, 2011 Kilroy Realty, L.P. [Member] Line of Credit [Member]	Sep. 30, 2011 Kilroy Realty, L.P. [Member]		Sep. 30, 2010 Kilroy Realty, L.P. [Member]	Dec. 31, 2010 Kilroy Realty, L.P. [Member]
Subsequent Events (Textuals) [Abstract]
Secured Debt	$ 473,997,000		$ 313,009,000	$ 68,700,000	$ 52,000,000				$ 473,997,000			$ 313,009,000
Debt Instrument, Maturity Date				Dec. 27, 2011	Apr. 01, 2012
Aggregate dividends, distributions, and dividend equivalents paid to common stockholders and common unitholders	58,942,000	50,299,000				21,400,000			58,942,000		50,299,000
Non-refundable escrow deposits related to potential future acquisitions	11,000,000						25,000,000
Credit Facility	$ 0		$ 159,000,000					$ 165,000,000	$ 0	[1]		$ 159,000,000

[1] As of September 30, 2011, there were no borrowings outstanding on the Credit Facility.