CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
REAL ESTATE ASSETS (Notes 2 and 3):
Land and improvements	$ 1,702,423	$ 1,628,848
Buildings and improvements	7,282,341	6,783,092
Undeveloped land and construction in progress	2,237,742	1,778,106
Total real estate assets held for investment	11,222,506	10,190,046
Accumulated depreciation and amortization	(1,962,730)	(1,798,646)
Total real estate assets held for investment, net	9,259,776	8,391,400
CASH AND CASH EQUIVALENTS	348,417	731,991
RESTRICTED CASH (Note 2)	13,042	91,139
MARKETABLE SECURITIES (Note 12)	27,285	27,481
CURRENT RECEIVABLES, NET	11,646	12,007
DEFERRED RENT RECEIVABLES, NET	394,297	386,658
DEFERRED LEASING COSTS AND ACQUISITION-RELATED INTANGIBLE ASSETS, NET (Note 2)	229,334	210,949
RIGHT OF USE GROUND LEASE ASSETS (Notes 2 and 11)	127,657	95,523
PREPAID EXPENSES AND OTHER ASSETS, NET (Note 4)	60,063	53,560
TOTAL ASSETS	10,471,517	10,000,708
LIABILITIES:
Secured debt, net (Notes 5 and 12)	249,690	253,582
Unsecured debt, net (Notes 5, 12 and 17)	3,673,183	3,670,099
Accounts payable, accrued expenses and other liabilities	441,357	445,100
Ground lease liabilities (Notes 2 and 11)	125,676	97,778
Accrued dividends and distributions (Note 17)	61,845	59,431
Deferred revenue and acquisition-related intangible liabilities, net (Note 2)	160,687	128,523
Rents received in advance and tenant security deposits	68,441	68,874
Total liabilities	4,780,879	4,723,387
COMMITMENTS AND CONTINGENCIES (Note 11)
Stockholders’ Equity (Note 6):
Common stock, $.01 par value, 280,000,000 shares authorized, 116,461,683 and 116,035,827 shares issued and outstanding, respectively	1,165	1,160
Additional paid-in capital	5,146,049	5,131,916
Retained earnings (distributions in excess of earnings)	297,250	(103,133)
Total stockholders’ equity	5,444,464	5,029,943
Noncontrolling Interests (Notes 1 and 7):
Common units of the Operating Partnership	53,788	49,875
Noncontrolling interests in consolidated property partnerships	192,386	197,503
Total noncontrolling interests	246,174	247,378
Total equity	5,690,638	5,277,321
TOTAL LIABILITIES AND EQUITY (CAPITAL)	10,471,517	10,000,708
Kilroy Realty L.P. [Member]
REAL ESTATE ASSETS (Notes 2 and 3):
Land and improvements	1,702,423	1,628,848
Buildings and improvements	7,282,341	6,783,092
Undeveloped land and construction in progress	2,237,742	1,778,106
Total real estate assets held for investment	11,222,506	10,190,046
Accumulated depreciation and amortization	(1,962,730)	(1,798,646)
Total real estate assets held for investment, net	9,259,776	8,391,400
CASH AND CASH EQUIVALENTS	348,417	731,991
RESTRICTED CASH (Note 2)	13,042	91,139
MARKETABLE SECURITIES (Note 12)	27,285	27,481
CURRENT RECEIVABLES, NET	11,646	12,007
DEFERRED RENT RECEIVABLES, NET	394,297	386,658
DEFERRED LEASING COSTS AND ACQUISITION-RELATED INTANGIBLE ASSETS, NET (Note 2)	229,334	210,949
RIGHT OF USE GROUND LEASE ASSETS (Notes 2 and 11)	127,657	95,523
PREPAID EXPENSES AND OTHER ASSETS, NET (Note 4)	60,063	53,560
TOTAL ASSETS	10,471,517	10,000,708
LIABILITIES:
Secured debt, net (Notes 5 and 12)	249,690	253,582
Unsecured debt, net (Notes 5, 12 and 17)	3,673,183	3,670,099
Accounts payable, accrued expenses and other liabilities	441,357	445,100
Ground lease liabilities (Notes 2 and 11)	125,676	97,778
Accrued dividends and distributions (Note 17)	61,845	59,431
Deferred revenue and acquisition-related intangible liabilities, net (Note 2)	160,687	128,523
Rents received in advance and tenant security deposits	68,441	68,874
Total liabilities	4,780,879	4,723,387
COMMITMENTS AND CONTINGENCIES (Note 11)
Noncontrolling Interests (Notes 1 and 7):
Common units, 116,461,683 and 116,035,827 held by the general partner and 1,150,574 and 1,150,574 held by common limited partners issued and outstanding, respectively (Note 7)	5,498,252	5,079,818
Noncontrolling interests in consolidated property partnerships (Note 1)	192,386	197,503
Total capital	5,690,638	5,277,321
TOTAL LIABILITIES AND EQUITY (CAPITAL)	$ 10,471,517	$ 10,000,708