Pro Forma Results of the Operating Partnership (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	10 Months Ended	12 Months Ended			10 Months Ended	12 Months Ended																					7 Months Ended		12 Months Ended	7 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member]	Dec. 31, 2011 Kilroy Realty, L.P. [Member]	Dec. 31, 2010 Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Pro Forma 2012 Material Acquisitions [Member]	Dec. 31, 2012 Pro Forma 2012 Material Acquisitions [Member] Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Pro Forma Information Including 2011 Acquisitions [Member]		Dec. 31, 2011 Pro Forma Information Including 2011 Acquisitions [Member]		Dec. 31, 2012 Pro Forma Information Including 2011 Acquisitions [Member] Kilroy Realty, L.P. [Member]		Dec. 31, 2011 Pro Forma Information Including 2011 Acquisitions [Member] Kilroy Realty, L.P. [Member]		Dec. 31, 2011 Pro Forma Information Including 2011 and 2010 Acquisitions [Member]		Dec. 31, 2010 Pro Forma Information Including 2011 and 2010 Acquisitions [Member]		Dec. 31, 2011 Pro Forma Information Including 2011 and 2010 Acquisitions [Member] Kilroy Realty, L.P. [Member]		Dec. 31, 2010 Pro Forma Information Including 2011 and 2010 Acquisitions [Member] Kilroy Realty, L.P. [Member]		Dec. 31, 2011 Pro Forma 2011 Material Acquisitions [Member]		Dec. 31, 2011 Pro Forma 2011 Material Acquisitions [Member]	Dec. 31, 2011 Pro Forma 2011 Material Acquisitions [Member] Kilroy Realty, L.P. [Member]		Dec. 31, 2011 Pro Forma 2011 Material Acquisitions [Member] Kilroy Realty, L.P. [Member]
Pro Forma Results of the Operating Partnership
Revenues											$ 414,813		$ 363,815		$ 414,813		$ 363,815		$ 377,871		$ 283,941		$ 377,871		$ 283,941
Net income available to common unitholders											238,947	[1],[2]	42,601	[1],[2]	244,337	[3],[4]	43,386	[3],[4]	41,293	[1],[2],[5]	2,491	[1],[2],[5]	42,039	[3],[4],[6]	2,437	[3],[4],[6]
Net income available to common unitholders per unit - basic											$ 3.41	[1],[2]	$ 0.73	[1],[2]	$ 3.40	[3],[4]	$ 0.72	[3],[4]	$ 0.71	[1],[2],[5]	$ 0.03	[1],[2],[5]	$ 0.70	[3],[4],[6]	$ 0.03	[3],[4],[6]
Net income available to common unitholders per unit - diluted											$ 3.41	[1],[2]	$ 0.73	[1],[2]	$ 3.40	[3],[4]	$ 0.72	[3],[4]	$ 0.71	[1],[2],[5]	$ 0.03	[1],[2],[5]	$ 0.70	[3],[4],[6]	$ 0.03	[3],[4],[6]
Actual results for material acquisitions
Revenues	18,943				18,943																						15,150			15,150
Net income	3,412				3,412																						397	[7]		397	[7]
Pro Forma Results of the Operating Partnership (Textuals) [Abstract]
Acquisition-related expenses		$ 4,937	$ 4,053	$ 2,248		$ 4,937	$ 4,053	$ 2,248	$ 1,000	$ 1,000																			$ 600			$ 600

[1] The pro forma results for all periods presented include incremental interest expense assuming the acquisitions were funded by pro forma borrowings under the revolving credit facility. The pro forma interest expense estimate is calculated based on the actual interest rate in effect on the revolving credit facility for each respective period. A portion of the 599 N. Mathilda Avenue, Sunnyvale, CA total purchase price related to development assets acquired. This portion of the purchase price has no pro forma impact as the interest expense related to development would be capitalized and would not impact net income available to common stockholders. Actual funding of the acquisitions may be from different sources and the pro forma borrowings and related pro forma interest expense estimate assumed herein are not indicative of actual results.

[2] The pro forma results for the year ended December 31, 2012 were adjusted to exclude acquisition-related expenses of approximately $1.0 million incurred in 2012 for the acquisition of 4100-4700 Bohannon Drive, Menlo Park, CA , 10900 Northeast 4th Street, Bellevue, WA and 555-599 N. Mathilda Avenue, Sunnyvale, CA. The pro forma results for the year ended December 31, 2011 were adjusted to include these expenses.

[3] The pro forma results for all periods presented include incremental interest expense assuming the acquisitions were funded by pro forma borrowings under the revolving credit facility. The pro forma interest expense estimate is calculated based on the actual interest rate in effect on the revolving credit facility for each respective period. A portion of the 599 N. Mathilda Avenue, Sunnyvale, CA total purchase price related to development assets acquired. This portion of the purchase price has no pro forma impact as the interest expense related to development would be capitalized and would not impact net income available to stockholders. Actual funding of the acquisitions may be from different sources and the pro forma borrowings and related pro forma interest expense estimate assumed herein are not indicative of actual results.

[4] The pro forma results for the year ended December 31, 2012 were adjusted to exclude acquisition-related expenses of approximately $1.0 million incurred in 2012 for the acquisitions of 4100-4700 Bohannon Drive, Menlo Park, CA and 10900 Northeast 4th Street, Bellevue, WA and 555-599 N. Mathilda Avenue, Sunnyvale, CA. The pro forma results for the year ended December 31, 2011 were adjusted to include these expenses.

[5] The pro forma results for the year ended December 31, 2011 were adjusted to exclude acquisition-related expenses of approximately $0.6 million incurred in 2011 for the acquisitions of 601 108th Avenue N.E., Bellevue, WA, and 201 Third Street, San Francisco, CA. The pro forma results for the year ended December 31, 2010 were adjusted to include these expenses.

[6] The pro forma results for the year ended December 31, 2011 were adjusted to exclude acquisition-related expenses of approximately $0.6 million incurred in 2011 for the acquisitions of 601 108th Avenue N.E., Bellevue, WA, and 201 Third Street, San Francisco, CA. The pro forma results for the year ended December 31, 2010 were adjusted to include these expenses.

[7] Reflects the net operating income less depreciation for these properties and amortization of lease related intangibles.