Preferred and Common Units of the Operating Partnership (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Accrued distributions
Accrued dividends and distributions	$ 28,924		$ 22,692
Summary of units
Common units held by limited partners	1,826,503		1,718,131
Restricted Stock Units (RSUs) [Member]
Accrued distributions
Accrued dividends and distributions	367	[1]	295	[1]
Kilroy Realty, L.P. [Member]
Accrued distributions
Accrued dividends and distributions	28,924		22,692
Summary of units
Common units held by general partner	74,926,981		58,819,717
Common units held by limited partners	1,826,503		1,718,131
Kilroy Realty, L.P. [Member] | Restricted Stock Units (RSUs) [Member]
Accrued distributions
Accrued dividends and distributions	367	[2]	295	[2]
Summary of units
RSUs	1,048,863		842,675
Kilroy Realty, L.P. [Member] | Partners Capital Common Unit [Member]
Accrued distributions
Accrued dividends and distributions	27,230		21,483
Kilroy Realty, L.P. [Member] | Partners Capital General Partner [Member]
Accrued distributions
Accrued dividends and distributions	26,224		20,587
Kilroy Realty, L.P. [Member] | Partners Capital Limited Partner [Member]
Accrued distributions
Accrued dividends and distributions	639		601
Kilroy Realty, L.P. [Member] | Partners Capital Preferred Units [Member]
Accrued distributions
Accrued dividends and distributions	$ 1,694		$ 1,209
Kilroy Realty, L.P. [Member] | Series E Cumulative Redeemable Preferred Unit [Member]
Summary of units
Preferred units outstanding			1,610,000
Kilroy Realty, L.P. [Member] | Series F Cumulative Redeemable Preferred Unit [Member]
Summary of units
Preferred units outstanding			3,450,000
Kilroy Realty, L.P. [Member] | Series G Cumulative Redeemable Preferred Unit [Member]
Summary of units
Preferred units outstanding	4,000,000
Kilroy Realty, L.P. [Member] | Series H Cumulative Redeemable Preferred Unit [Member]
Summary of units
Preferred units outstanding	4,000,000

[1] The amount includes the value of the dividend equivalents that will be paid with additional fully-vested RSUs (see Note 12)

[2] The amount includes the value of the dividend equivalents that will be paid with additional fully-vested RSUs (see Note 12).