Kilroy Realty (KRC) 10-K 15 Feb 19 2018 Q4 Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 08, 2019	Jun. 30, 2018
Entity Information [Line Items]
Entity Registrant Name	KILROY REALTY CORP
Entity Central Index Key	1,025,996
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q4
Amendment Flag	false
Smaller Reporting Company	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		100,964,220
Entity Public Float			$ 7,557,990,980
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Shell Company	false
Kilroy Realty L.P. [Member]
Entity Information [Line Items]
Entity Registrant Name	Kilroy Realty, L.P.
Entity Central Index Key	1,493,976
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q4
Amendment Flag	false
Smaller Reporting Company	false
Entity Emerging Growth Company	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Shell Company	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
REAL ESTATE ASSETS
Land and improvements	$ 1,160,138	$ 1,076,172
Buildings and improvements	5,207,984	4,908,797
Undeveloped land and construction in progress	2,058,510	1,432,808
Total real estate assets held for investment	8,426,632	7,417,777
Accumulated depreciation and amortization	(1,391,368)	(1,264,162)
Total real estate assets held for investment, net	7,035,264	6,153,615
CASH AND CASH EQUIVALENTS	51,604	57,649
RESTRICTED CASH	119,430	9,149
MARKETABLE SECURITIES	21,779	20,674
CURRENT RECEIVABLES, NET	20,176	16,926
DEFERRED RENT RECEIVABLES, NET	267,007	246,391
DEFERRED LEASING COSTS AND ACQUISITION-RELATED INTANGIBLE ASSETS, NET	197,574	183,728
PREPAID EXPENSES AND OTHER ASSETS, NET	52,873	114,706
TOTAL ASSETS	7,765,707	6,802,838
LIABILITIES:
Secured debt, net	335,531	340,800
Unsecured debt, net	2,552,070	2,006,263
Unsecured line of credit	45,000	0
Accounts payable, accrued expenses and other liabilities	374,415	249,637
Accrued dividends and distributions	47,559	43,448
Deferred revenue and acquisition-related intangible liabilities, net	149,646	145,890
Rents received in advance and tenant security deposits	60,225	56,484
Total liabilities	3,564,446	2,842,522
COMMITMENTS AND CONTINGENCIES
Stockholders’ Equity:
Common stock, $.01 par value, 150,000,000 shares authorized, 100,746,988 and 98,620,333 shares issued and outstanding, respectively	1,007	986
Additional paid-in capital	3,976,953	3,822,492
Distributions in excess of earnings	(48,053)	(122,685)
Total stockholders’ equity	3,929,907	3,700,793
Noncontrolling Interests
Common units of the Operating Partnership	78,991	77,948
Noncontrolling interests in consolidated property partnerships	192,363	181,575
Total noncontrolling interests	271,354	259,523
Total equity	4,201,261	3,960,316
TOTAL LIABILITIES AND EQUITY/CAPITAL	$ 7,765,707	$ 6,802,838

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Common stock, par value (in dollars per share)	$ 0.01
Common Stock [Member]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued (in shares)	100,746,988	98,620,333
Common stock, shares outstanding	100,746,988	98,620,333

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
REVENUES:
Revenues	$ 747,298	$ 719,001	$ 642,572
EXPENSES:
Real estate taxes	70,820	66,449	55,206
Provision for bad debts	5,685	3,269	0
Ground leases	6,176	6,337	3,439
General and administrative expenses	90,471	60,581	57,029
Acquisition-related expenses	0	0	1,902
Depreciation and amortization	254,281	245,886	217,234
Total expenses	561,220	512,493	448,742
OTHER (EXPENSES) INCOME:
Interest income and other net investment gain/loss	(559)	5,503	1,764
Interest expense	(49,721)	(66,040)	(55,803)
Loss on early extinguishment of debt	(12,623)	(5,312)	0
Net gain (loss) on sales of land	11,825	449	(295)
Gains on sales of depreciable operating properties	142,926	39,507	164,302
Total other income (expenses)	91,848	(25,893)	109,968
NET INCOME	277,926	180,615	303,798
Net income attributable to noncontrolling common units of the Operating Partnership	(5,193)	(3,223)	(6,635)
Net income attributable to noncontrolling interests in consolidated property partnerships	(14,318)	(12,780)	(3,375)
Total income attributable to noncontrolling interests	(19,511)	(16,003)	(10,010)
NET INCOME ATTRIBUTABLE TO KILROY REALTY CORPORATION / KILROY REALTY, L.P.	258,415	164,612	293,788
Preferred dividends	0	(5,774)	(13,250)
Original issuance costs of redeemed preferred stock and preferred units	0	(7,589)	0
Total preferred dividends	0	(13,363)	(13,250)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS/UNITHOLDERS	$ 258,415	$ 151,249	$ 280,538
Net income available to common stockholders per share - basic (in dollars per share)	$ 2.56	$ 1.52	$ 3
Net income available to common stockholders per share - diluted (in dollars per share)	$ 2.55	$ 1.51	$ 2.97
Weighted average shares of common stock outstanding – basic (in shares)	99,972,359	98,113,561	92,342,483
Weighted average shares of common stock outstanding – diluted (in shares)	100,482,365	98,727,331	93,023,034
Rental [Member]
REVENUES:
Revenues	$ 656,631	$ 633,896	$ 574,413
Tenant reimbursements [Member]
REVENUES:
Revenues	80,982	76,559	61,079
Other property income [Member]
REVENUES:
Revenues	9,685	8,546	7,080
Real estate [Member]
EXPENSES:
Property expenses	$ 133,787	$ 129,971	$ 113,932

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Total Stockholders' Equity	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Distributions in Excess of Earnings [Member]	Noncontrolling Interests [Member]
Beginning Balance at Dec. 31, 2015	$ 3,234,586	$ 3,170,966	$ 192,411	$ 923	$ 3,047,894	$ (70,262)	$ 63,620
Beginning balance, shares outstanding (in shares) at Dec. 31, 2015				92,258,690
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	303,798	293,788				293,788	10,010
Issuance of common stock	31,117	31,117		$ 4	31,113
Issuance of common stock (in shares)				451,398
Issuance of share-based compensation awards	1,827	1,827			1,827
Non-cash amortization of share-based compensation	26,624	26,624			26,624
Exercise of stock options	12,208	12,208		$ 3	12,205
Exercise of stock options (in shares)				286,500
Repurchase of common stock, stock options and restricted stock units	(8,875)	(8,875)		$ (1)	(8,874)
Repurchase of common stock, stock options and restricted stock units (in shares)				(137,126)
Settlement of restricted stock units for shares of common stock	0	0		$ 1	(1)
Settlement of restricted stock units for shares of common stock (in shares)				109,044
Issuance of common units in connection with acquisition	48,033						48,033
Exchange of common units of the Operating Partnership	0	8,893		$ 2	8,891		(8,893)
Exchange of common units of the Operating Partnership (in shares)				250,933
Contributions from noncontrolling interests in consolidated property partnerships	453,449	328,997			328,997		124,452
Distributions to noncontrolling interests in consolidated property partnerships	(3,615)						(3,615)
Adjustment for noncontrolling interest in the Operating Partnership	0	8,973			8,973		(8,973)
Preferred dividends and distributions	(13,250)	(13,250)				(13,250)
Dividends declared per share of common stock and common unit	(326,585)	(318,273)				(318,273)	(8,312)
Ending Balance at Dec. 31, 2016	3,759,317	3,542,995	192,411	$ 932	3,457,649	(107,997)	216,322
Ending balance, shares outstanding (in shares) at Dec. 31, 2016				93,219,439
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	180,615	164,612				164,612	16,003
Redemption of Series G & H Preferred stock	(200,000)	(200,000)	(192,411)			(7,589)
Issuance of common stock	326,058	326,058		$ 46	326,012
Issuance of common stock (in shares)				4,662,577
Issuance of share-based compensation awards	5,890	5,890			5,890
Non-cash amortization of share-based compensation	26,319	26,319			26,319
Exercise of stock options	12,179	12,179		$ 4	12,175
Exercise of stock options (in shares)				285,000
Repurchase of common stock, stock options and restricted stock units	(12,986)	(12,986)		$ (2)	(12,984)
Repurchase of common stock, stock options and restricted stock units (in shares)				(168,881)
Settlement of restricted stock units for shares of common stock	0			$ 3	(3)
Settlement of restricted stock units for shares of common stock (in shares)				317,848
Exchange of common units of the Operating Partnership	0	10,939		$ 3	10,936		(10,939)
Exchange of common units of the Operating Partnership (in shares)				304,350
Contributions from noncontrolling interests in consolidated property partnerships	54,604						54,604
Distributions to noncontrolling interests in consolidated property partnerships	(16,542)						(16,542)
Adjustment for noncontrolling interest in the Operating Partnership	0	(3,502)			(3,502)		3,502
Preferred dividends and distributions	(5,774)	(5,774)				(5,774)
Dividends declared per share of common stock and common unit	(169,364)	(165,937)				(165,937)	(3,427)
Ending Balance at Dec. 31, 2017	3,960,316	3,700,793	0	$ 986	3,822,492	(122,685)	259,523
Ending balance, shares outstanding (in shares) at Dec. 31, 2017				98,620,333
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	277,926	258,415				258,415	19,511
Issuance of common stock	130,693	130,693		$ 18	130,675
Issuance of common stock (in shares)				1,817,195
Issuance of share-based compensation awards	3,926	3,926			3,926
Non-cash amortization of share-based compensation	35,890	35,890			35,890
Exercise of stock options	41	41		$ 0	41
Exercise of stock options (in shares)				1,000
Repurchase of common stock, stock options and restricted stock units	(16,553)	(16,553)		$ (2)	(16,551)
Repurchase of common stock, stock options and restricted stock units (in shares)				(231,800)
Settlement of restricted stock units for shares of common stock	0			$ 4	(4)
Settlement of restricted stock units for shares of common stock (in shares)				488,354
Exchange of common units of the Operating Partnership	0	1,962		$ 1	1,961		(1,962)
Exchange of common units of the Operating Partnership (in shares)				51,906
Contributions from noncontrolling interests in consolidated property partnerships	8,273						8,273
Distributions to noncontrolling interests in consolidated property partnerships	(11,803)						(11,803)
Adjustment for noncontrolling interest in the Operating Partnership	0	(1,477)			(1,477)		1,477
Dividends declared per share of common stock and common unit	(187,448)	(183,783)				(183,783)	(3,665)
Ending Balance at Dec. 31, 2018	$ 4,201,261	$ 3,929,907	$ 0	$ 1,007	$ 3,976,953	$ (48,053)	$ 271,354
Ending balance, shares outstanding (in shares) at Dec. 31, 2018				100,746,988

Consolidated Statements of Eq_2

Consolidated Statements of Equity (Parenthetical) - $ / shares	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Dividends declared per common share (in dollars per share)	$ 0.375	$ 0.375	$ 1.79000	$ 1.65	$ 3.375

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 277,926	$ 180,615	$ 303,798
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of real estate assets and leasing costs	249,882	241,862	213,156
Depreciation of non-real estate furniture, fixtures and equipment	4,400	4,024	4,078
Increase in provision for bad debts	5,685	3,269	0
Non-cash amortization of share-based compensation awards	27,932	19,046	21,064
Non-cash amortization of deferred financing costs and net debt discounts	1,084	3,247	2,720
Non-cash amortization of net below market rents	(9,748)	(8,528)	(7,166)
Loss on early extinguishment of debt	12,623	5,312	0
(Gain) loss on sale of land	(11,825)	(449)	295
Gains on sales of depreciable operating properties	(142,926)	(39,507)	(164,302)
Non-cash amortization of deferred revenue related to tenant-funded tenant improvements	(18,429)	(16,767)	(13,244)
Straight-line rents	(26,976)	(33,275)	(29,629)
Net change in other operating assets	(7,930)	(17,732)	(5,214)
Net change in other operating liabilities	48,345	5,895	19,498
Net cash provided by operating activities	410,043	347,012	345,054
CASH FLOWS FROM INVESTING ACTIVITIES:
Expenditures for development properties and undeveloped land	(489,236)	(397,440)	(351,012)
Expenditures for acquisitions of development properties and undeveloped land	(311,299)	(19,829)	(33,513)
Expenditures for acquisitions of operating properties	(257,340)	0	(393,767)
Expenditures for operating properties and other capital assets	(166,440)	(88,425)	(111,961)
Net proceeds received from dispositions	364,300	182,492	325,031
Decrease (increase) in acquisition-related deposits	36,000	(35,900)	1,902
Proceeds received from repayment of note receivable	15,100	0	0
Issuance of notes receivable	0	0	(16,100)
Net cash used in investing activities	(808,915)	(359,102)	(579,420)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net proceeds from issuance of common stock	130,693	326,058	31,117
Redemption of Series G and H Preferred stock	0	(200,000)	0
Net proceeds from the issuance of unsecured debt	648,537	674,447	0
Repayments of unsecured debt	(261,823)	(519,024)	0
Borrowings on unsecured revolving credit facility	765,000	270,000	305,000
Repayments on unsecured revolving credit facility	(690,000)	(270,000)	(305,000)
Borrowings on unsecured debt	120,000	0	0
Principal payments and repayments of secured debt	(3,584)	(130,371)	(74,140)
Proceeds from the issuance of secured debt	0	0	170,000
Financing costs	(6,262)	(11,500)	(2,159)
Repurchase of common stock and restricted stock units	(16,553)	(12,986)	(8,875)
Proceeds from exercise of stock options	41	12,179	12,208
Contributions from noncontrolling interests in consolidated property partnerships	8,273	54,604	453,449
Distributions to noncontrolling interests in consolidated property partnerships	(11,803)	(16,542)	(3,615)
Dividends and distributions paid to common stockholders and common unitholders	(179,411)	(340,697)	(137,444)
Dividends and distributions paid to preferred stockholders and preferred unitholders	0	(7,409)	(13,250)
Net cash provided by (used in) financing activities	503,108	(171,241)	427,291
Net increase (decrease) in cash and cash equivalents and restricted cash	104,236	(183,331)	192,925
Cash and cash equivalents and restricted cash, beginning of year	66,798	250,129	57,204
Cash and cash equivalents and restricted cash, end of year	$ 171,034	$ 66,798	$ 250,129

Consolidated Balance Sheets (KI

Consolidated Balance Sheets (KILROY REALTY, L.P.) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
REAL ESTATE ASSETS
Land and improvements	$ 1,160,138	$ 1,076,172
Buildings and improvements	5,207,984	4,908,797
Undeveloped land and construction in progress	2,058,510	1,432,808
Total real estate assets held for investment	8,426,632	7,417,777
Accumulated depreciation and amortization	(1,391,368)	(1,264,162)
Total real estate assets held for investment, net	7,035,264	6,153,615
CASH AND CASH EQUIVALENTS	51,604	57,649
RESTRICTED CASH	119,430	9,149
MARKETABLE SECURITIES	21,779	20,674
CURRENT RECEIVABLES, NET	20,176	16,926
DEFERRED RENT RECEIVABLES, NET	267,007	246,391
DEFERRED LEASING COSTS AND ACQUISITION-RELATED INTANGIBLE ASSETS, NET	197,574	183,728
PREPAID EXPENSES AND OTHER ASSETS, NET	52,873	114,706
TOTAL ASSETS	7,765,707	6,802,838
LIABILITIES:
Secured debt, net	335,531	340,800
Unsecured debt, net	2,552,070	2,006,263
Unsecured line of credit	45,000	0
Accounts payable, accrued expenses and other liabilities	374,415	249,637
Accrued distributions	47,559	43,448
Deferred revenue and acquisition-related intangible liabilities, net	149,646	145,890
Rents received in advance and tenant security deposits	60,225	56,484
Total liabilities	3,564,446	2,842,522
COMMITMENTS AND CONTINGENCIES
Partners’ Capital:
TOTAL LIABILITIES AND EQUITY/CAPITAL	7,765,707	6,802,838
Kilroy Realty L.P. [Member]
REAL ESTATE ASSETS
Land and improvements	1,160,138	1,076,172
Buildings and improvements	5,207,984	4,908,797
Undeveloped land and construction in progress	2,058,510	1,432,808
Total real estate assets held for investment	8,426,632	7,417,777
Accumulated depreciation and amortization	(1,391,368)	(1,264,162)
Total real estate assets held for investment, net	7,035,264	6,153,615
CASH AND CASH EQUIVALENTS	51,604	57,649
RESTRICTED CASH	119,430	9,149
MARKETABLE SECURITIES	21,779	20,674
CURRENT RECEIVABLES, NET	20,176	16,926
DEFERRED RENT RECEIVABLES, NET	267,007	246,391
DEFERRED LEASING COSTS AND ACQUISITION-RELATED INTANGIBLE ASSETS, NET	197,574	183,728
PREPAID EXPENSES AND OTHER ASSETS, NET	52,873	114,706
TOTAL ASSETS	7,765,707	6,802,838
LIABILITIES:
Secured debt, net	335,531	340,800
Unsecured debt, net	2,552,070	2,006,263
Unsecured line of credit	45,000	0
Accounts payable, accrued expenses and other liabilities	374,415	249,637
Accrued distributions	47,559	43,448
Deferred revenue and acquisition-related intangible liabilities, net	149,646	145,890
Rents received in advance and tenant security deposits	60,225	56,484
Total liabilities	3,564,446	2,842,522
COMMITMENTS AND CONTINGENCIES
Partners’ Capital:
Common units, 100,746,988 and 98,620,333 held by the general partner and 2,025,287 and 2,077,193 held by common limited partners issued and outstanding, respectively	4,003,700	3,773,941
Total partners’ capital	4,003,700	3,773,941
Noncontrolling interests in consolidated property partnerships and subsidiaries (Notes 2 and 12)	197,561	186,375
Total capital	4,201,261	3,960,316
TOTAL LIABILITIES AND EQUITY/CAPITAL	$ 7,765,707	$ 6,802,838

Consolidated Balance Sheets (_2

Consolidated Balance Sheets (KILROY REALTY, L.P.) (Parenthetical) - Kilroy Realty L.P. [Member] - Capital units [Member] - shares	Dec. 31, 2018	Dec. 31, 2017
General partner, units issued (in units)	100,746,988	98,620,333
General partner, units outstanding (in units)	100,746,988	98,620,333
Limited partner, units issued (in units)	2,025,287	2,077,193
Limited partner, units outstanding (in units)	2,025,287	2,077,193

Consolidated Statements of Op_2

Consolidated Statements of Operations (KILROY REALTY, L.P.) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
REVENUES:
Revenues	$ 747,298	$ 719,001	$ 642,572
EXPENSES:
Real estate taxes	70,820	66,449	55,206
Provision for bad debts	5,685	3,269	0
Ground leases	6,176	6,337	3,439
General and administrative expenses	90,471	60,581	57,029
Depreciation and amortization	254,281	245,886	217,234
Total expenses	561,220	512,493	448,742
OTHER (EXPENSES) INCOME:
Interest income and other net investment gain/loss	(559)	5,503	1,764
Interest expense	(49,721)	(66,040)	(55,803)
Loss on early extinguishment of debt	(12,623)	(5,312)	0
Net gain (loss) on sales of land	11,825	449	(295)
Gains on sales of depreciable operating properties	142,926	39,507	164,302
Total other income (expenses)	91,848	(25,893)	109,968
NET INCOME	277,926	180,615	303,798
Net income attributable to noncontrolling interests in consolidated property partnerships and subsidiaries	(19,511)	(16,003)	(10,010)
NET INCOME ATTRIBUTABLE TO KILROY REALTY CORPORATION / KILROY REALTY, L.P.	258,415	164,612	293,788
Preferred dividends	0	(5,774)	(13,250)
Original issuance costs of redeemed preferred stock and preferred units	0	(7,589)	0
Total preferred distributions	0	(13,363)	(13,250)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS/UNITHOLDERS	$ 258,415	$ 151,249	$ 280,538
Net income available to common unitholders per unit (in dollars per unit)	$ 2.56	$ 1.52	$ 3
Net income available to common unitholders per unit (in dollars per unit)	$ 2.55	$ 1.51	$ 2.97
Weighted average common units outstanding - basic (in shares)	99,972,359	98,113,561	92,342,483
Weighted average common units outstanding - diluted (in shares)	100,482,365	98,727,331	93,023,034
Rental [Member]
REVENUES:
Revenues	$ 656,631	$ 633,896	$ 574,413
Tenant reimbursements [Member]
REVENUES:
Revenues	80,982	76,559	61,079
Other property income [Member]
REVENUES:
Revenues	9,685	8,546	7,080
Real estate [Member]
EXPENSES:
Property expenses	133,787	129,971	113,932
Kilroy Realty L.P. [Member]
REVENUES:
Revenues	747,298	719,001	642,572
EXPENSES:
Real estate taxes	70,820	66,449	55,206
Provision for bad debts	5,685	3,269	0
Ground leases	6,176	6,337	3,439
General and administrative expenses	90,471	60,581	57,029
Acquisition-related expenses	0	0	1,902
Depreciation and amortization	254,281	245,886	217,234
Total expenses	561,220	512,493	448,742
OTHER (EXPENSES) INCOME:
Interest income and other net investment gain/loss	(559)	5,503	1,764
Interest expense	(49,721)	(66,040)	(55,803)
Loss on early extinguishment of debt	(12,623)	(5,312)	0
Net gain (loss) on sales of land	11,825	449	(295)
Gains on sales of depreciable operating properties	142,926	39,507	164,302
Total other income (expenses)	91,848	(25,893)	109,968
NET INCOME	277,926	180,615	303,798
Net income attributable to noncontrolling interests in consolidated property partnerships and subsidiaries	(14,716)	(13,175)	(3,735)
NET INCOME ATTRIBUTABLE TO KILROY REALTY CORPORATION / KILROY REALTY, L.P.	263,210	167,440	300,063
Preferred dividends	0	(5,774)	(13,250)
Original issuance costs of redeemed preferred stock and preferred units	0	(7,589)	0
Total preferred distributions	0	(13,363)	(13,250)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS/UNITHOLDERS	$ 263,210	$ 154,077	$ 286,813
Net income available to common unitholders per unit (in dollars per unit)	$ 2.56	$ 1.52	$ 2.99
Net income available to common unitholders per unit (in dollars per unit)	$ 2.55	$ 1.51	$ 2.96
Weighted average common units outstanding - basic (in shares)	102,025,276	100,246,567	94,771,688
Weighted average common units outstanding - diluted (in shares)	102,535,282	100,860,337	95,452,239
Kilroy Realty L.P. [Member] | Rental [Member]
REVENUES:
Revenues	$ 656,631	$ 633,896	$ 574,413
Kilroy Realty L.P. [Member] | Tenant reimbursements [Member]
REVENUES:
Revenues	80,982	76,559	61,079
Kilroy Realty L.P. [Member] | Other property income [Member]
REVENUES:
Revenues	9,685	8,546	7,080
Kilroy Realty L.P. [Member] | Real estate [Member]
EXPENSES:
Property expenses	$ 133,787	$ 129,971	$ 113,932

Consolidated Statements of Capi

Consolidated Statements of Capital (KILROY REALTY, L.P.) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 166,890	$ 40,971	$ 32,540	$ 37,281	$ 277,926	$ 180,615	$ 303,798
Redemption of Series G & H Preferred stock						(200,000)
Issuance of common units in connection with acquisition							48,033
Non-cash amortization of share-based compensation					35,890	26,319	26,624
Settlement of restricted stock units for shares of common stock					0	0	0
Distributions to noncontrolling interests in consolidated property partnerships					(11,803)	(16,542)	(3,615)
Preferred dividends and distributions						(5,774)	(13,250)
Noncontrolling Interest In Consolidated Subsidiaries [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income					19,511	16,003	10,010
Issuance of common units in connection with acquisition							48,033
Distributions to noncontrolling interests in consolidated property partnerships					(11,803)	(16,542)	(3,615)
Kilroy Realty L.P. [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		3,960,316		3,759,317	3,960,316	3,759,317	3,234,586
Net income	166,890	40,971	32,540	37,281	277,926	180,615	303,798
Redemption of Series G & H Preferred stock						(200,000)
Issuance of common units					130,693	326,058	31,117
Issuance of common units in connection with acquisition							48,033
Issuance of share-based compensation awards					3,926	5,890	1,827
Non-cash amortization of share-based compensation					35,890	26,319	26,624
Exercise of stock options					41	12,179	12,208
Repurchase of common units and restricted stock units					(16,553)	(12,986)	(8,875)
Settlement of restricted stock units for shares of common stock					0	0	0
Contribution by noncontrolling interest in consolidated subsidiary					8,273	54,604	453,449
Distributions to noncontrolling interests in consolidated property partnerships					(11,803)	(16,542)	(3,615)
Preferred dividends and distributions						(5,774)	(13,250)
Distributions declared per common unit					(187,448)	(169,364)	(326,585)
Ending balance	4,201,261		3,960,316		4,201,261	3,960,316	3,759,317
Kilroy Realty L.P. [Member] | Total Partners Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		3,773,941		3,624,179	3,773,941	3,624,179	3,224,020
Net income					263,210	167,440	300,063
Redemption of Series G & H Preferred stock						(200,000)
Issuance of common units					130,693	326,058	31,117
Issuance of common units in connection with acquisition							48,033
Issuance of share-based compensation awards					3,926	5,890	1,827
Non-cash amortization of share-based compensation					35,890	26,319	26,624
Exercise of stock options					41	12,179	12,208
Repurchase of common units and restricted stock units					(16,553)	(12,986)	(8,875)
Settlement of restricted stock units for shares of common stock						0	0
Contribution by noncontrolling interest in consolidated subsidiary					0	0	328,997
Preferred dividends and distributions						(5,774)	(13,250)
Distributions declared per common unit					(187,448)	(169,364)	(326,585)
Ending balance	4,003,700		3,773,941		4,003,700	3,773,941	3,624,179
Kilroy Realty L.P. [Member] | Partners Capital Preferred Units [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		0		192,411	0	192,411	192,411
Redemption of Series G & H Preferred stock						(192,411)
Ending balance	0		0		0	0	192,411
Kilroy Realty L.P. [Member] | Partners Capital Common Unit [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		$ 3,773,941		$ 3,431,768	$ 3,773,941	$ 3,431,768	$ 3,031,609
Beginning balance units (in units)		100,697,526		95,600,982	100,697,526	95,600,982	94,023,465
Net income					$ 263,210	$ 167,440	$ 300,063
Redemption of Series G & H Preferred stock						(7,589)
Issuance of common units					$ 130,693	$ 326,058	$ 31,117
Issuance of common units (in units)					1,817,195	4,662,577	451,398
Issuance of common units in connection with acquisition							$ 48,033
Issuance of common units in connection with acquisition (in units)							867,701
Issuance of share-based compensation awards					$ 3,926	$ 5,890	$ 1,827
Non-cash amortization of share-based compensation					35,890	26,319	26,624
Exercise of stock options					$ 41	$ 12,179	$ 12,208
Exercise of stock options (in units)					1,000	285,000	286,500
Repurchase of common units and restricted stock units					$ (16,553)	$ (12,986)	$ (8,875)
Repurchase of common units and restricted stock units (in units)					(231,800)	(168,881)	(137,126)
Settlement of restricted stock units for shares of common stock					$ 0	$ 0	$ 0
Settlement of restricted stock units for shares of common stock (in units)					488,354	317,848	109,044
Contribution by noncontrolling interest in consolidated subsidiary					$ 0		$ 328,997
Preferred dividends and distributions						(5,774)	(13,250)
Distributions declared per common unit					(187,448)	(169,364)	(326,585)
Ending balance	$ 4,003,700		$ 3,773,941		$ 4,003,700	$ 3,773,941	$ 3,431,768
Ending balance units (in units)	102,772,275		100,697,526		102,772,275	100,697,526	95,600,982
Kilroy Realty L.P. [Member] | Noncontrolling Interest In Consolidated Subsidiaries [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		$ 186,375		$ 135,138	$ 186,375	$ 135,138	$ 10,566
Net income					14,716	13,175	3,735
Contribution by noncontrolling interest in consolidated subsidiary					8,273	54,604	124,452
Distributions to noncontrolling interests in consolidated property partnerships					(11,803)	(16,542)	(3,615)
Ending balance	$ 197,561		$ 186,375		$ 197,561	$ 186,375	$ 135,138

Consolidated Statements of Ca_2

Consolidated Statements of Capital (KILROY REALTY, L.P.) - Parenthetical - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Kilroy Realty L.P. [Member]
Distributions declared per common unit (in dollars per units)	$ 1.79000	$ 1.65000	$ 3.375

Consolidated Statements of Ca_3

Consolidated Statements of Cash Flows (KILROY REALTY, L.P.) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 277,926	$ 180,615	$ 303,798
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of real estate assets and leasing costs	249,882	241,862	213,156
Depreciation of non-real estate furniture, fixtures and equipment	4,400	4,024	4,078
Increase in provision for bad debts	5,685	3,269	0
Non-cash amortization of share-based compensation awards	27,932	19,046	21,064
Non-cash amortization of deferred financing costs and net debt discounts	1,084	3,247	2,720
Non-cash amortization of net below market rents	(9,748)	(8,528)	(7,166)
Loss on early extinguishment of debt	12,623	5,312	0
(Gain) loss on sale of land	(11,825)	(449)	295
Gains on sales of depreciable operating properties	(142,926)	(39,507)	(164,302)
Non-cash amortization of deferred revenue related to tenant-funded tenant improvements	(18,429)	(16,767)	(13,244)
Straight-line rents	(26,976)	(33,275)	(29,629)
Net change in other operating assets	(7,930)	(17,732)	(5,214)
Net change in other operating liabilities	48,345	5,895	19,498
Net cash provided by operating activities	410,043	347,012	345,054
CASH FLOWS FROM INVESTING ACTIVITIES:
Expenditures for development properties and undeveloped land	(489,236)	(397,440)	(351,012)
Expenditures for acquisitions of development properties and undeveloped land	(311,299)	(19,829)	(33,513)
Expenditures for acquisitions of operating properties	(257,340)	0	(393,767)
Expenditures for operating properties and other capital assets	(166,440)	(88,425)	(111,961)
Net proceeds received from dispositions	364,300	182,492	325,031
Decrease (increase) in acquisition-related deposits	36,000	(35,900)	1,902
Proceeds received from repayment of note receivable	15,100	0	0
Issuance of notes receivable	0	0	(16,100)
Net cash used in investing activities	(808,915)	(359,102)	(579,420)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net proceeds from issuance of common stock	130,693	326,058	31,117
Redemption of Series G and H Preferred stock	0	(200,000)	0
Net proceeds from the issuance of unsecured debt	648,537	674,447	0
Repayments of unsecured debt	(261,823)	(519,024)	0
Borrowings on unsecured revolving credit facility	765,000	270,000	305,000
Repayments on unsecured revolving credit facility	(690,000)	(270,000)	(305,000)
Borrowings on unsecured debt	120,000	0	0
Principal payments and repayments of secured debt	(3,584)	(130,371)	(74,140)
Proceeds from the issuance of secured debt	0	0	170,000
Financing costs	(6,262)	(11,500)	(2,159)
Repurchase of common stock and restricted stock units	(16,553)	(12,986)	(8,875)
Proceeds from exercise of stock options	41	12,179	12,208
Contributions from noncontrolling interests in consolidated property partnerships	8,273	54,604	453,449
Distributions to noncontrolling interests in consolidated property partnerships	(11,803)	(16,542)	(3,615)
Distributions paid to common unitholders	(179,411)	(340,697)	(137,444)
Distributions paid to preferred unitholders	0	(7,409)	(13,250)
Net cash provided by (used in) financing activities	503,108	(171,241)	427,291
Net increase (decrease) in cash and cash equivalents and restricted cash	104,236	(183,331)	192,925
Cash and cash equivalents and restricted cash, beginning of year	66,798	250,129	57,204
Cash and cash equivalents and restricted cash, end of year	171,034	66,798	250,129
Kilroy Realty L.P. [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	277,926	180,615	303,798
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of real estate assets and leasing costs	249,882	241,862	213,156
Depreciation of non-real estate furniture, fixtures and equipment	4,400	4,024	4,078
Increase in provision for bad debts	5,685	3,269	0
Non-cash amortization of share-based compensation awards	27,932	19,046	21,064
Non-cash amortization of deferred financing costs and net debt discounts	1,084	3,247	2,720
Non-cash amortization of net below market rents	(9,748)	(8,528)	(7,166)
Loss on early extinguishment of debt	12,623	5,312	0
(Gain) loss on sale of land	(11,825)	(449)	295
Gains on sales of depreciable operating properties	(142,926)	(39,507)	(164,302)
Non-cash amortization of deferred revenue related to tenant-funded tenant improvements	(18,429)	(16,767)	(13,244)
Straight-line rents	(26,976)	(33,275)	(29,629)
Net change in other operating assets	(7,930)	(17,732)	(5,214)
Net change in other operating liabilities	48,345	5,895	19,498
Net cash provided by operating activities	410,043	347,012	345,054
CASH FLOWS FROM INVESTING ACTIVITIES:
Expenditures for development properties and undeveloped land	(489,236)	(397,440)	(351,012)
Expenditures for acquisitions of development properties and undeveloped land	(311,299)	(19,829)	(33,513)
Expenditures for acquisitions of operating properties	(257,340)	0	(393,767)
Expenditures for operating properties and other capital assets	(166,440)	(88,425)	(111,961)
Net proceeds received from dispositions	364,300	182,492	325,031
Decrease (increase) in acquisition-related deposits	36,000	(35,900)	1,902
Proceeds received from repayment of note receivable	15,100	0	0
Issuance of notes receivable	0	0	(16,100)
Net cash used in investing activities	(808,915)	(359,102)	(579,420)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net proceeds from issuance of common stock	130,693	326,058	31,117
Redemption of Series G and H Preferred stock	0	(200,000)	0
Net proceeds from the issuance of unsecured debt	648,537	674,447	0
Repayments of unsecured debt	(261,823)	(519,024)	0
Borrowings on unsecured revolving credit facility	765,000	270,000	305,000
Repayments on unsecured revolving credit facility	(690,000)	(270,000)	(305,000)
Borrowings on unsecured debt	120,000	0	0
Principal payments and repayments of secured debt	(3,584)	(130,371)	(74,140)
Proceeds from the issuance of secured debt	0	0	170,000
Financing costs	(6,262)	(11,500)	(2,159)
Repurchase of common stock and restricted stock units	(16,553)	(12,986)	(8,875)
Proceeds from exercise of stock options	41	12,179	12,208
Contributions from noncontrolling interests in consolidated property partnerships	8,273	54,604	453,449
Distributions to noncontrolling interests in consolidated property partnerships	(11,803)	(16,542)	(3,615)
Distributions paid to common unitholders	(179,411)	(340,697)	(137,444)
Distributions paid to preferred unitholders	0	(7,409)	(13,250)
Net cash provided by (used in) financing activities	503,108	(171,241)	427,291
Net increase (decrease) in cash and cash equivalents and restricted cash	104,236	(183,331)	192,925
Cash and cash equivalents and restricted cash, beginning of year	66,798	250,129	57,204
Cash and cash equivalents and restricted cash, end of year	$ 171,034	$ 66,798	$ 250,129

Organization and Ownership

Organization and Ownership	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Ownership	Organization and Ownership Kilroy Realty Corporation (the “Company”) is a self-administered real estate investment trust (“REIT”) active in premier office and mixed-use submarkets along the West Coast. We own, develop, acquire and manage real estate assets, consisting primarily of Class A properties in the coastal regions of Greater Los Angeles, Orange County, San Diego County, the San Francisco Bay Area and Greater Seattle, which we believe have strategic advantages and strong barriers to entry. Class A real estate encompasses attractive and efficient buildings of high quality that are attractive to tenants, are well-designed and constructed with above-average material, workmanship and finishes and are well-maintained and managed. We qualify as a REIT under the Internal Revenue Code of 1986, as amended (the “Code”). The Company’s common stock is publicly traded on the New York Stock Exchange (“NYSE”) under the ticker symbol “KRC.” We own our interests in all of our real estate assets through Kilroy Realty, L.P. (the “Operating Partnership”) and Kilroy Realty Finance Partnership, L.P. (the “Finance Partnership”). We generally conduct substantially all of our operations through the Operating Partnership. Unless stated otherwise or the context indicates otherwise, the terms “Kilroy Realty Corporation” or the “Company,” “we,” “our,” and “us” refer to Kilroy Realty Corporation and its consolidated subsidiaries and the term “Operating Partnership” refers to Kilroy Realty, L.P. and its consolidated subsidiaries. The descriptions of our business, employees, and properties apply to both the Company and the Operating Partnership. Our stabilized portfolio of operating properties was comprised of the following properties at December 31, 2018 : Number of Buildings Rentable Square Feet (unaudited) Number of Tenants Percentage Occupied (unaudited) Percentage Leased (unaudited) Stabilized Office Properties 94 13,232,580 482 94.4 % 96.6 % Number of Number of Units 2018 Average Occupancy Stabilized Residential Property 1 200 79.7 % Our stabilized portfolio includes all of our properties with the exception of development and redevelopment properties currently committed for construction, under construction or in the tenant improvement phase, undeveloped land and real estate assets held for sale. We define redevelopment properties as those properties for which we expect to spend significant development and construction costs on the existing or acquired buildings pursuant to a formal plan, the intended result of which is a higher economic return on the property. We define properties in the tenant improvement phase as properties that we are developing or redeveloping where the project has reached cold shell condition and is ready for tenant improvements, which may require additional major base building construction before being placed in service. Projects in the tenant improvement phase are added to our stabilized portfolio once the project reaches the earlier of 95% occupancy or one year from the date of the cessation of major base building construction activities. Costs capitalized to construction in progress for development and redevelopment properties are transferred to land and improvements, buildings and improvements, and deferred leasing costs on our consolidated balance sheets at the historical cost of the property as the projects are placed in service. As of December 31, 2018 , the following properties were excluded from our stabilized portfolio. We did not have any redevelopment properties or properties held for sale at December 31, 2018 . Number of Properties/Projects Estimated Rentable Square Feet (1) (unaudited) In-process development projects - tenant improvement (2) 2 1,150,000 In-process development projects - under construction (3) 3 1,290,000 _______________ (1) Estimated rentable square feet upon completion. (2) Includes 88,000 square feet of Production, Distribution, and Repair (“PDR”) space. (3) In addition to the estimated office and PDR rentable square feet noted above, development projects under construction also include 96,000 square feet of retail space and 801 residential units. Our stabilized portfolio also excludes our future development pipeline, which as of December 31, 2018 was comprised of five potential development sites, representing approximately 73 gross acres of undeveloped land. As of December 31, 2018 , all of our properties and development projects were owned and all of our business was conducted in the state of California with the exception of eight office properties and one development project under construction located in the state of Washington. All of our properties and development projects are 100% owned, excluding four office properties owned by three consolidated property partnerships and an office property held by a consolidated variable interest entity for a transaction intended to qualify as a like-kind exchange pursuant to Section 1031 of the Code (“Section 1031 Exchange”) that closed in January 2019. Two of the three property partnerships, 100 First Street Member, LLC (“100 First LLC”) and 303 Second Street Member, LLC (“303 Second LLC”), each owned one office property in San Francisco, California through subsidiary REITs. As of December 31, 2018 , the Company owned a 56% common equity interest in both 100 First LLC and 303 Second LLC. The third property partnership, Redwood City Partners, LLC (“Redwood LLC”) owned two office properties in Redwood City, California. As of December 31, 2018 , the Company owned an approximate 93% common equity interest in Redwood LLC. The remaining interests in all three property partnerships were owned by unrelated third parties. As of December 31, 2018 , the Company owned an approximate 98.0% common general partnership interest in the Operating Partnership. The remaining approximate 2.0% common limited partnership interest in the Operating Partnership as of December 31, 2018 was owned by non-affiliated investors and certain of our executive officers and directors. Both the general and limited common partnership interests in the Operating Partnership are denominated in common units. Generally, the number of common units held by the Company is equivalent to the number of outstanding shares of the Company’s common stock, and the rights of all the common units to quarterly distributions and payments in liquidation mirror those of the Company’s common stockholders. The common limited partners have certain redemption rights as provided in the Operating Partnership’s Seventh Amended and Restated Agreement of Limited Partnership, as amended, the “Partnership Agreement”. Kilroy Realty Finance, Inc., which is a wholly-owned subsidiary of the Company, is the sole general partner of the Finance Partnership and owns a 1.0% common general partnership interest in the Finance Partnership. The Operating Partnership owns the remaining 99.0% common limited partnership interest. With the exception of the Operating Partnership and our consolidated property partnerships, all of our subsidiaries are wholly-owned.

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Basis of Presentation and Significant Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	Basis of Presentation and Significant Accounting Policies Basis of Presentation The consolidated financial statements of the Company include the consolidated financial position and results of operations of the Company, the Operating Partnership, the Finance Partnership, 303 Second LLC, 100 First LLC, Redwood LLC and all of our wholly-owned and controlled subsidiaries. The consolidated financial statements of the Operating Partnership include the consolidated financial position and results of operations of the Operating Partnership, the Finance Partnership, 303 Second LLC, 100 First LLC, Redwood LLC and all of our wholly-owned and controlled subsidiaries. All intercompany balances and transactions have been eliminated in the consolidated financial statements. Accounting Pronouncements Adopted January 1, 2018 Effective January 1, 2018, we adopted Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) No. 2014-09 “Revenue From Contracts with Customers (Topic 606)” (“ASU 2014-09”) and the related FASB ASU Nos. 2016-12 and 2016-20, which provide practical expedients, technical corrections, and improvements for certain aspects of ASU 2014-09, on a modified retrospective basis. ASU 2014-09 establishes a single comprehensive model for entities to use in accounting for revenue from contracts with customers and supersedes most of the existing revenue recognition guidance. We evaluated each of the Company’s revenue streams to determine the sources of revenue that are impacted by ASU 2014-09 and concluded that two revenue streams, sales of real estate and revenue from our multi-tenant parking arrangements, fall within the scope of Topic 606. We evaluated the impact of the adoption of the guidance on the timing of gain recognition for our historical dispositions and concluded there was not a significant impact to our consolidated financial statements given the straight forward nature of our historical disposition transactions. We also evaluated the impact of the guidance on the timing and pattern of revenue recognition for our multi-tenant parking arrangements and determined there was no significant impact to our consolidated financial statements. We generally provide parking for our multi-tenant properties based on the prevailing market rate per parking space, which adjusts based on prevailing market rates during the tenant’s occupancy, and we recognize parking revenue as parking spaces are utilized by the tenant. Given the structure of these arrangements whereby the amount of parking revenue we recognize corresponds directly to the tenant’s use, we were able to apply the practical expedient provided in Accounting Standards Codification (“ASC”) 606-10-50-14(b) (the “right to invoice” practical expedient). As a result of applying this practical expedient, we are not required to disclose the transaction price allocated to future performance obligations for multi-tenant parking since we cannot predict or estimate the use of such parking spaces. During the years ended December 31, 2018 , 2017 and 2016 , we recognized $26.7 million , $26.7 million and $23.3 million , respectively, of parking revenue for arrangements that are within the scope of Topic 606, which is included in rental revenues on our consolidated statements of operations. We concluded that the adoption of Topic 606 did not have a material impact on our consolidated financial statements or a material impact on the notes to our consolidated financial statements. Effective January 1, 2018, we adopted FASB ASU No. 2017-09 “Compensation - Stock Compensation (Topic 718)” on a prospective basis. Under the guidance, an entity will not apply modification accounting to a share-based payment award if the award’s fair value, vesting conditions, and classification as an equity or liability instrument remain the same immediately before and after the change. The adoption of this guidance did not have an impact on our consolidated financial statements or notes to our consolidated financial statements. Effective January 1, 2018, we adopted FASB ASU No. 2017-05 “Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20)” (“ASU 2017-05”) on a retrospective basis. This standard clarifies the scope of the original guidance within Subtopic 610-20 “Gains and Losses from the Derecognition of Nonfinancial Assets” that was issued in connection with ASU 2014-09 which provided guidance for recognizing gains and losses from the transfer of nonfinancial assets in transactions with noncustomers. Additionally, ASU 2017-05 adds guidance pertaining to the partial sales of real estate and clarifies that nonfinancial assets within the scope of ASC 610-20 may include nonfinancial assets transferred within a legal entity to a counterparty. For example, a parent may transfer control of nonfinancial assets by transferring ownership interests in a consolidated subsidiary. We evaluated the impact of the new amendments on our historical transactions and concluded that there was no impact. As such, the adoption of this guidance did not have an impact on our consolidated financial statements or notes to our consolidated financial statements. Effective January 1, 2018, we adopted FASB ASU No. 2016-15 (“ASU 2016-15”) which provides guidance where there is diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows, on a retrospective basis. The adoption of this guidance did not have an impact on our consolidated financial statements or notes to our consolidated financial statements. Effective January 1, 2018, we adopted FASB ASU No. 2016-01 (“ASU 2016-01”) which amends the accounting guidance on the classification and measurement of financial instruments and FASB ASU No. 2018-03 (“ASU 2018-03”) which provides technical corrections and improvements to ASU 2016-01, on a modified retrospective basis. The amendments require that all investments in equity securities, including other ownership interests, are reported at fair value with changes in fair value reported in net income. This requirement does not apply to investments that qualify for equity method accounting or to those that result in consolidation of the investee or for which the entity has elected the predictability exception to fair value measurement. Additionally, the amendments require that the portion of the total fair value change caused by a change in instrument-specific credit risk for financial liabilities for which the fair value option has been elected would be recognized in other comprehensive income. Any accumulated amount remaining in other comprehensive income is reclassified to earnings when the liability is extinguished. The adoption of this guidance did not have an impact on our consolidated financial statements or notes to our consolidated financial statements since our only financial instruments within the scope of ASU 2016-01 and 2018-03 are the marketable securities related to our deferred compensation plan which are classified as trading securities and marked to market at fair value through earnings each reporting period. Partially Owned Entities and Variable Interest Entities At December 31, 2018 the consolidated financial statements of the Company included three VIEs in addition to the Operating Partnership: 100 First LLC, 303 Second LLC and an entity established during the fourth quarter of 2018 to facilitate a Section 1031 Exchange. At December 31, 2018 , the Company and the Operating Partnership were determined to be the primary beneficiaries of these three VIEs since we had the ability to control the activities that most significantly impact each of the VIEs’ economic performance. As of December 31, 2018 , the three VIEs’ total assets, liabilities and noncontrolling interests included on our consolidated balance sheet were approximately $615.4 million (of which $543.9 million related to real estate held for investment), approximately $45.1 million and approximately $186.4 million , respectively. In January 2019, the Section 1031 Exchange was successfully completed and the related VIE was terminated. Revenues, income and net assets generated by 100 First LLC and 303 Second LLC may only be used to settle their contractual obligations, which primarily consist of operating expenses, capital expenditures and required distributions. At December 31, 2017 , the consolidated financial statements of the Company included two VIEs in addition to the Operating Partnership: 100 First LLC and 303 Second LLC. At December 31, 2017 , the impact of consolidating the VIEs increased the Company’s total assets, liabilities and noncontrolling interests on our consolidated balance sheet by approximately $426.5 million (of which $382.1 million related to real estate held for investment on our consolidated balance sheet), approximately $27.3 million and approximately $175.4 million , respectively. The consolidated financial statements of the Operating Partnership included the same three VIEs at December 31, 2017 . Our accounting policy is to consolidate entities in which we have a controlling financial interest and significant decision making control over the entity's operations. In determining whether we have a controlling financial interest in a partially owned entity and the requirement to consolidate the accounts of that entity, we consider factors such as ownership interest, board representation, management representation, size of our investment (including loans), authority to control decisions, and contractual and substantive participating rights of the members. In addition to evaluating control rights, we consolidate entities in which the other members have no substantive kick-out rights to remove the Company as the managing member. Entities in which the equity investors do not have sufficient equity at risk to finance their endeavors without additional financial support or the holders of the equity investment at risk do not have a controlling financial interest are VIEs. We evaluate whether an entity is a VIE and whether we are the primary beneficiary. We are deemed to be the primary beneficiary of a VIE when we have the power to direct the activities of the VIE that most significantly impact the VIEs’ economic performance and the obligation to absorb losses or receive benefits that could potentially be significant to the VIE. If the requirements for consolidation are not met, the Company would account for investments under the equity method of accounting if we have the ability to exercise significant influence over the entity. Equity method investments would be initially recorded at cost and subsequently adjusted for our share of net income or loss and cash contributions and distributions each period. The Company did not have any equity method investments at December 31, 2018 or 2017 . Significant Accounting Policies Acquisitions Subsequent to our adoption of FASB ASU No. 2017-01 (“ASU 2017-01”) on January 1, 2017, which was adopted on a prospective basis, acquisitions of operating properties and development and redevelopment opportunities generally no longer meet the definition of a business and are accounted for as asset acquisitions. For these asset acquisitions, we record the acquired tangible and intangible assets and assumed liabilities based on each asset’s and liability’s relative fair value at the acquisition date of the total purchase price plus any capitalized acquisition costs. We record the acquired tangible and intangible assets and assumed liabilities of acquisitions of operating properties and development and redevelopment opportunities that meet the accounting criteria to be accounted for as business combinations at fair value at the acquisition date. The acquired assets and assumed liabilities for an acquisition generally include but are not limited to (i) land and improvements, buildings and improvements, undeveloped land and construction in progress and (ii) identified tangible and intangible assets and liabilities associated with in-place leases, including tenant improvements, leasing costs, value of above-market and below-market operating leases and ground leases, acquired in-place lease values and tenant relationships, if any. Any debt assumed and equity (including common units of the Operating Partnership) issued in connection with a property acquisition is recorded at fair value on the date of acquisition. The fair value of land and improvements is derived from comparable sales of land and improvements within the same submarket and/or region. The fair value of buildings and improvements, tenant improvements and leasing costs considers the value of the property as if it was vacant as well as current replacement costs and other relevant market rate information. The fair value of the above-market or below-market component of an acquired in-place operating lease is based upon the present value (calculated using a market discount rate) of the difference between (i) the contractual rents to be paid pursuant to the lease over its remaining non-cancellable lease term and (ii) our estimate of the rents that would be paid using fair market rental rates and rent escalations at the date of acquisition measured over the remaining non-cancellable term of the lease for above-market operating leases and the initial non-cancellable term plus the term of any below-market fixed rate renewal options, if applicable, for below-market operating leases. Our below-market operating leases generally do not include fixed rate or below-market renewal options. The amounts recorded for above-market operating leases are included in deferred leasing costs and acquisition-related intangible assets, net on the balance sheet and are amortized on a straight-line basis as a reduction of rental income over the remaining term of the applicable leases. The amounts recorded for below-market operating leases are included in deferred revenue and acquisition-related intangible liabilities, net on the balance sheet and are amortized on a straight-line basis as an increase to rental income over the remaining term of the applicable leases plus the term of any below-market fixed rate renewal options, if applicable. The amortization of the below-market ground lease obligation is recorded as an increase to ground lease expense in the consolidated statements of operations for the periods presented. The amortization of the above-market ground lease obligation is recorded as a decrease to ground lease expense in the consolidated statements of operations for the periods presented. The fair value of acquired in-place leases is derived based on our assessment of lost revenue and costs incurred for the period required to lease the “assumed vacant” property to the occupancy level when purchased. The amount recorded for acquired in-place leases is included in deferred leasing costs and acquisition-related intangible assets, net on the balance sheet and amortized as an increase to depreciation and amortization expense over the remaining term of the applicable leases. Fully amortized intangible assets are written off each quarter. Subsequent to our adoption of ASU 2017-01 on January 1, 2017, transaction costs associated with our acquisitions are capitalized as part of the purchase price of the acquisition. Prior to our adoption of ASU 2017-01, costs associated with all operating property acquisitions and those development and redevelopment acquisitions that met the criteria to be accounted for as business combinations were expensed as incurred and costs associated with development acquisitions accounted for as asset acquisitions were capitalized as part of the cost of the asset. Operating Properties Operating properties are generally carried at historical cost less accumulated depreciation. Properties held for sale are reported at the lower of the carrying value or the fair value less estimated cost to sell. The cost of operating properties includes the purchase price or development costs of the properties. Costs incurred for the renovation and betterment of the operating properties are capitalized to our investment in that property. Maintenance and repairs are charged to expense as incurred. When evaluating properties to be held and used for potential impairment, we first evaluate whether there are any indicators of impairment for any of our properties. If any impairment indicators are present for a specific property, we then evaluate the regional market conditions that could reasonably affect the property. If there are negative changes and trends in that regional market, we then perform an undiscounted cash flow analysis and compare the net carrying amount of the property to the property’s estimated undiscounted future cash flow over the anticipated holding period. If the estimated undiscounted future cash flow is less than the net carrying amount of the property, we then perform an impairment loss calculation to determine if the fair value of the property is less than the net carrying value of the property. Our impairment loss calculation compares the net carrying amount of the property to the property’s estimated fair value, which may be based on estimated discounted future cash flow calculations or third-party valuations or appraisals. We would recognize an impairment loss if the asset’s net carrying amount exceeds the asset’s estimated fair value. If we were to recognize an impairment loss, the estimated fair value of the asset (less costs to sell for assets held for sale) would become its new cost basis. For a depreciable long-lived asset, the new cost basis would be depreciated (amortized) over the remaining useful life of that asset. Cost Capitalization All costs clearly associated with the development, redevelopment and construction of a property are capitalized as project costs, including internal compensation costs. In addition, the following costs are capitalized as project costs during periods in which activities necessary to prepare development and redevelopment properties for their intended use are in progress: pre-construction costs essential to the development of the property, interest, real estate taxes and insurance. • For office and retail development and redevelopment properties that are pre-leased, we cease capitalization when revenue recognition commences, which is upon substantial completion of tenant improvements deemed to be the Company’s asset for accounting purposes. • For office and retail development and redevelopment properties that are not pre-leased, we may not immediately build out the tenant improvements. Therefore, we cease capitalization when revenue recognition commences upon substantial completion of the tenant improvements deemed to be the Company's asset for accounting purposes, but in any event, no later than one year after the cessation of major construction activities. We also cease capitalization on a development or redevelopment property when activities necessary to prepare the property for its intended use have been suspended. • For office and retail development or redevelopment properties with multiple tenants and staged leasing, we cease capitalization and begin depreciation on the portion of the development or redevelopment property for which revenue recognition has commenced. • For residential development properties, we cease capitalization when the property is substantially complete and available for occupancy. Once major base building construction activities have ceased and the development or redevelopment property is placed in service, the costs capitalized to construction in progress are transferred to land and improvements, buildings and improvements, and deferred leasing costs on our consolidated balance sheets as the historical cost of the property. Depreciation and Amortization of Buildings and Improvements The costs of buildings and improvements and tenant improvements are depreciated using the straight-line method of accounting over the estimated useful lives set forth in the table below. Depreciation expense for buildings and improvements for the three years ended December 31, 2018 , 2017 , and 2016 was $198.6 million , $190.5 million , and $172.0 million , respectively. Asset Description Depreciable Lives Buildings and improvements 25 – 40 years Tenant improvements 1 – 20 years (1) ________________________ (1) Tenant improvements are amortized over the shorter of the lease term or the estimated useful life. Real Estate Assets Held for Sale, Dispositions and Discontinued Operations A real estate asset is classified as held for sale when certain criteria are met, including but not limited to the availability of the asset for immediate sale, the existence of an active program to locate a buyer and the probable sale or transfer of the asset within one year. If such criteria are met, we present the applicable assets and liabilities related to the real estate asset held for sale, if material, separately on the balance sheet and we would cease to record depreciation and amortization expense. Real estate assets held for sale are reported at the lower of their carrying value or their estimated fair value less the estimated costs to sell. As of December 31, 2018 and 2017 , we did not have any properties classified as held for sale. Property disposals representing a strategic shift that have (or will have) a major effect on the Company’s operations and financial results, such as a major line of business, a major geographical area or a major equity investment, are required to be presented as discontinued operations. If we were to determine that a property disposition represents a strategic shift, the revenues, expenses and net gain (loss) on dispositions of the property would be recorded in discontinued operations for all periods presented through the date of the applicable disposition. The operations of the eleven , eleven and six properties sold during the years ended December 31, 2018 , December 31, 2017 and December 31, 2016 , respectively, are presented in continuing operations as they did not represent a strategic shift in the Company’s operations and financial results. The net gains (losses) on dispositions of non-depreciable real estate property, including land, are reported in the consolidated statements of operations as gains (losses) on sale of land within continuing operations in the period the land is sold. The net gains (losses) on dispositions of depreciable real estate property are reported in the consolidated statements of operations as gains on sales of depreciable operating properties within continuing operations in the period the land is sold. Revenue Recognition We recognize revenue from rent, tenant reimbursements, parking and other revenue once all of the following criteria are met: (i) the agreement has been fully executed and delivered, (ii) services have been rendered, (iii) the amount is fixed or determinable and (iv) the collectability of the amount is reasonably assured. Minimum annual rental revenues are recognized in rental revenues on a straight-line basis over the non-cancellable term of the related lease. Rental revenue recognition commences when the tenant takes possession or controls the physical use of the leased space. In order for the tenant to take possession, the leased space must be substantially complete and ready for its intended use. In order to determine whether the leased space is substantially ready for its intended use, we begin by determining whether the Company or the tenant owns the tenant improvements. When we conclude that the Company is the owner of tenant improvements, rental revenue recognition begins when the tenant takes possession of the finished space, which is generally when Company owned tenant improvements are substantially complete. In certain instances, when we conclude that the Company is not the owner (the tenant is the owner) of tenant improvements, rental revenue recognition begins when the tenant takes possession of or controls the space. When we conclude that the Company is the owner of tenant improvements, we record the cost to construct the tenant improvements, including costs paid for or reimbursed by the tenants, as a capital asset. For these tenant improvements, we record the amount funded by or reimbursed by the tenants as deferred revenue, which is amortized on a straight-line basis as additional rental income over the term of the related lease. When we conclude that the tenant is the owner of tenant improvements for accounting purposes, we record our contribution towards those improvements as a lease incentive, which is included in deferred leasing costs and acquisition-related intangible assets, net on our consolidated balance sheets and amortized as a reduction to rental income on a straight-line basis over the term of the lease. For residential properties, we commence revenue recognition upon lease commencement. Residential rental revenue is recognized on a straight-line basis over the term of the related lease, net of any concessions. Tenant Reimbursements Reimbursements from tenants, consisting of amounts due from tenants for common area maintenance, real estate taxes and other recoverable costs, are recognized as revenue in the period the recoverable costs are incurred. Tenant reimbursements are generally recognized and recorded on a gross basis, as we are generally the primary obligor with respect to purchasing goods and services from third-party suppliers, have discretion in selecting the supplier, and have credit risk. Other Property Income Other property income primarily includes amounts recorded in connection with lease terminations, tenant bankruptcy settlement payments, broken deal income and property damage settlement related payments. Lease termination fees are amortized over the remaining lease term, if applicable. If there is no remaining lease term, they are recognized when received and realized. Other property income also includes miscellaneous income from tenants, such as fees related to the restoration of leased premises to their original condition and fees for late rental payments. Allowances for Uncollectible Tenant and Deferred Rent Receivables We carry our current and deferred rent receivables net of allowances for uncollectible amounts. Our determination of the adequacy of these allowances is based primarily upon evaluations of individual receivables, current economic conditions, and other relevant factors. The allowances are increased or decreased through the provision for bad debts on our consolidated statements of operations. We also evaluate allowances for all other receivables which includes note receivables included in prepaid expenses and other assets on our consolidated balances sheets. Cash and Cash Equivalents We consider all highly-liquid investments with original maturities of three months or less to be cash equivalents. Restricted Cash Restricted cash consists of cash proceeds from dispositions that are temporarily held at qualified intermediaries for purposes of facilitating potential Section 1031 Exchanges and cash held in escrow related to acquisition and disposition holdbacks. Restricted cash also includes cash held as collateral to provide credit enhancement for the Operating Partnership’s mortgage debt, including cash reserves for capital expenditures, tenant improvements and property taxes. As of December 31, 2018 we had $113.1 million of restricted cash held at qualified intermediaries for the purpose of facilitating Section 1031 Exchanges. In January 2019, the Section 1031 Exchange was completed and the cash proceeds were released from the qualified intermediary. We did not have any restricted cash held at qualified intermediaries for the purpose of facilitating Section 1031 Exchanges at December 31, 2017 . Marketable Securities / Deferred Compensation Plan Marketable securities reported in our consolidated balance sheets represent the assets held in connection with the Kilroy Realty Corporation 2007 Deferred Compensation Plan (the “Deferred Compensation Plan”) (see Note 16 “Employee Benefit Plans” for additional information). The Deferred Compensation Plan assets are held in a limited rabbi trust and invested in various mutual and money market funds. As a result, the marketable securities are treated as trading securities for financial reporting purposes and are adjusted to fair value at the end of each accounting period, with the corresponding gains and losses recorded in interest income and other net investment gains (losses). At the time eligible management employees (“Participants”) defer compensation or earn mandatory Company contributions, or if we were to make a discretionary contribution, we record compensation cost and a corresponding deferred compensation plan liability, which is included in accounts payable, accrued expenses, and other liabilities on our consolidated balance sheets. This liability is adjusted to fair value at the end of each accounting period based on the performance of the benchmark funds selected by each Participant, and the impact of adjusting the liability to fair value is recorded as an increase or decrease to compensation cost. The impact of adjusting the deferred compensation plan liability to fair value and the changes in the value of the marketable securities held in connection with the Deferred Compensation Plan generally offset and therefore do not significantly impact net income. Deferred Leasing Costs Costs incurred in connection with successful property leasing are capitalized as deferred leasing costs and classified as investing activities in the statement of cash flows. Deferred leasing costs consist primarily of leasing commissions and also include certain internal payroll costs and lease incentives, which are amortized using the straight-line method of accounting over the lives of the leases which generally range from one to 20 years. We reevaluate the remaining useful lives of leasing costs as the creditworthiness of our tenants and economic and market conditions change. If we determine that the estimated remaining life of a lease has changed, we adjust the amortization period accordingly. Fully amortized deferred leasing costs are written off each quarter. As discussed below under “ Accounting Standards Issued But Not Yet Effective at December 31, 2018 ,” upon the adoption of FASB ASU No. 2016-02 “Leases (Topic 842),” most deferred leasing costs (with the exception of leasing commissions paid to external third party brokers) will no longer meet the criteria for capitalization. For leases commenced prior to December 31, 2018, these costs will continue to be amortized over the remaining life of the associated lease. For leases executed prior to December 31, 2018 that have not yet commenced as of December 31, 2018, such costs will be charged to distributions in excess of earnings as of January 1, 2019. Deferred Financing Costs Financing costs related to the origination or assumption of long-term debt are deferred and generally amortized using the straight-line method of accounting, which approximates the effective interest method, over the contractual terms of the applicable financings. Fully amortized deferred financing costs are written off when the corresponding financing is repaid. Debt Discounts and Premiums Original issuance debt discounts and discounts/premiums related to recording debt acquired in connection with operating property acquisitions at fair value are generally amortized and accreted on a straight-line basis, which approximates the effective interest method. Discounts are recorded as additional interest expense from date of issuance or acquisition through the contractual maturity date of the related debt. Premiums are recorded as a reduction to interest expense from the date of issuance or acquisition through the contractual maturity date of the related debt. Noncontrolling Interests - Common Units of the Operating Partnership in the Company's Consolidated Financial Statements Common units of the Operating Partnership within noncontrolling interests in the Company’s consolidated financial statements represent the common limited partnership interests in the Operating Partnership not held by the Company (“noncontrolling common units”). Noncontrolling common units are presented in the equity section of the Company’s consolidated balance sheets and are reported at their proportionate share of the net assets of the Operating Partnership. Noncontrolling interests with redemption provisions that permit the issuer to settle in either cash or shares of common stock must be further evaluated to determine whether equity or temporary equi

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2018
Asset Acquisitions [Abstract]
Acquisitions	Acquisitions Operating Property Acquisitions During the year ended December 31, 2018, we acquired the four operating properties listed below in two transactions from unrelated third parties. We did not acquire any operating properties during the year ended December 31, 2017 . Property Date of Acquisition Number of Buildings Rentable Square Feet (unaudited) Occupancy as of December 31, 2018 (unaudited) Purchase Price (in millions) (1) 2018 Acquisitions 345, 347 & 349 Oyster Point Boulevard, South San Francisco, CA January 31, 2018 3 145,530 78.5 % $ 111.0 345 Brannan Street, San Francisco, CA (2) December 21, 2018 1 110,030 99.7 % 146.0 Total (3) 4 255,560 $ 257.0 ________________________ (1) Excludes acquisition-related costs. (2) At December 31, 2018 , this property was temporarily being held in a separate VIE to facilitate potential Section 1031 Exchanges. During January 2019, the Company completed the Section 1031 Exchange related to this VIE. See Note 2 “Basis of Presentation and Significant Accounting Policies.” (3) The results of operations for the properties acquired during 2018 contributed $8.0 million and $1.7 million to revenue and net income, respectively, for the year ended December 31, 2018. The related assets, liabilities and results of operations of the acquired properties are included in the consolidated financial statements as of the date of acquisition. The following table summarizes the estimated fair values of the assets and liabilities assumed at the respective acquisition dates for our 2018 operating property acquisitions: Total 2018 Operating Property Acquisitions (1) Assets Land and improvements $ 80,269 Buildings and improvements (2) 172,059 Deferred leasing costs and acquisition-related intangible assets (3) 13,593 Total assets acquired $ 265,921 Liabilities Acquisition-related intangible liabilities (4) $ 8,921 Total liabilities assumed 8,921 Net assets and liabilities acquired $ 257,000 ________________________ (1) The purchase price of the two acquisitions completed during the year ended December 31, 2018 were individually less than 5% and in aggregate less than 10% of the Company’s total assets as of December 31, 2017 . (2) Represents buildings, building improvements and tenant improvements. (3) Represents in-place leases (approximately $11.8 million with a weighted average amortization period of 1.3 years years) and leasing commissions (approximately $1.8 million with a weighted average amortization period of 6.6 years years). (4) Represents below-market leases (approximately $8.9 million with a weighted average amortization period of 9.8 years years). Development Project Acquisitions On June 1, 2018 , we acquired the following 39 -acre development site, which is located adjacent to the three operating properties we acquired in January 2018, from an unrelated third party. The acquisition was funded with proceeds from the Company’s unsecured revolving credit facility and the Company’s at-the-market stock offering program. Project Date of Acquisition City/Submarket Type Purchase Price (in millions) (1) Kilroy Oyster Point June 1, 2018 South San Francisco Land $ 308.2 ________________________ (1) Excludes acquisition-related costs. In connection with this acquisition, we also recorded $40.6 million in accrued liabilities and environmental remediation liabilities at the date of acquisition, which are not included in the purchase price above. As of December 31, 2018 , the purchase price and our current estimate of assumed liabilities are included in undeveloped land and construction in progress and the assumed liabilities are included in accounts payable, accrued expenses and other liabilities on the Company’s consolidated balance sheets. On October 10, 2017 , the Company completed the acquisition of a 1.2 acre development site located in the Little Italy neighborhood of downtown San Diego, California in three separate transactions from separate unrelated third parties for a total purchase price of $19.4 million and the assumption of $1.4 million of accrued liabilities. Acquisition Costs During the years ended December 31, 2018 , 2017 , and 2016 , we capitalized $3.8 million , $4.6 million , and $0.5 million , respectively, of acquisition costs. During the year ended December 31, 2016 , we expensed $1.9 million of acquisition costs.

Dispositions

Dispositions	12 Months Ended
	Dec. 31, 2018
Discontinued Operations and Disposal Groups [Abstract]
Dispositions	Dispositions Operating Property Dispositions The following table summarizes the operating properties sold during the years ended December 31, 2018 , 2017 and 2016 : Location Month of Disposition Number of Buildings Rentable Square Feet (unaudited) Sales Price (in millions) (1) 2018 Dispositions 1310-1327 Chesapeake Terrace, Sunnyvale, CA November 4 266,982 $ 160.3 Plaza Yarrow Bay Properties (2) November 4 279,924 134.5 23925, 23975, & 24025 Park Sorrento, Calabasas, CA December 3 225,340 78.2 Total 2018 Dispositions 11 772,246 $ 373.0 2017 Dispositions 5717 Pacific Center Boulevard, San Diego, CA January 1 67,995 $ 12.1 Sorrento Mesa and Mission Valley Properties (3) September 10 675,143 174.5 Total 2017 Dispositions 11 743,138 $ 186.6 2016 Dispositions Torrey Santa Fe Properties (4) January 4 465,812 $ 262.3 4930, 4939 & 4955 Directors Place, San Diego, CA (5) July 2 136,908 49.0 Total 2016 Dispositions 6 602,720 $ 311.3 __________________ (1) Represents gross sales price before the impact of broker commissions and closing costs. (2) The Plaza Yarrow Bay Properties include the following properties: 10210, 10220 and 10230 NE Points Drive & 3933 Lake Washington Boulevard NE in Kirkland, Washington. (3) The Sorrento Mesa and Mission Valley Properties includes the following properties: 10390, 10394, 10398, 10421, 10445 and 10455 Pacific Center Court, 2355, 2365, 2375 and 2385 Northside Drive and Pacific Corporate Center - Lot 8, a 5.0 acre undeveloped land parcel. (4) The Torrey Santa Fe Properties include the following properties: 7525, 7535, 7545 and 7555 Torrey Santa Fe. (5) Includes two operating properties totaling 136,908 rentable square feet and a 7.0 acre undeveloped land parcel. The total gains on the sales of the operating properties sold during the years ended December 31, 2018 , 2017 and 2016 were $142.9 million , $39.5 million and $164.3 million , respectively. Land Dispositions During the year ended December 31, 2018 , in connection with the Plaza Yarrow Bay Properties disposition listed above, we recognized a gain on sale of land of $11.8 million . During the year ended December 31, 2017 , in connection with the Sorrento Mesa and Mission Valley Properties disposition listed above, we recognized a gain on sale of land of $0.4 million . The following table summarizes the land dispositions completed during the year ended December 31, 2016 : Properties Submarket Month of Disposition Gross Site Acreage (unaudited) Sales Price (1) (in millions) 2016 Land Dispositions Carlsbad Oaks - Lot 7 Carlsbad January 7.6 $ 4.5 Carlsbad Oaks - Lots 4 & 5 Carlsbad June 11.2 6.0 Carlsbad Oaks - Lot 8 Carlsbad June 13.2 8.9 Total 2016 Land Dispositions (2)(3) 32.0 $ 19.4 __________________ (1) Represents gross sales price before the impact of commissions and closing costs. (2) In connection with these land dispositions, $2.3 million of secured debt was assumed by the buyers. (3) The 2016 land dispositions resulted in a net loss on sales of $0.3 million . Restricted Cash Related to Dispositions As of December 31, 2018 , approximately $113.1 million of net proceeds related to the operating property dispositions during the year ended December 31, 2018 were temporarily being held at a qualified intermediary at our direction, for the purpose of facilitating a Section 1031 Exchange. The cash proceeds were included in restricted cash on our consolidated balance sheets at December 31, 2018 . During January 2019, the Section 1031 Exchange related to this VIE was successfully completed and the cash proceeds were released from the qualified intermediary. We did not have any restricted cash related to dispositions or Section 1031 Exchanges as of December 31, 2017 .

Deferred Leasing Costs and Acqu

Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, net	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, net	Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, net The following table summarizes our deferred leasing costs and acquisition-related intangible assets (acquired value of leasing costs, above-market operating leases, in-place leases and below-market ground lease obligation) and intangible liabilities (acquired value of below-market operating leases and above-market ground lease obligation) as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Deferred Leasing Costs and Acquisition-related Intangible Assets, net: Deferred leasing costs $ 266,905 $ 248,598 Accumulated amortization (100,805 ) (101,917 ) Deferred leasing costs, net 166,100 146,681 Above-market operating leases 2,836 4,199 Accumulated amortization (2,150 ) (3,068 ) Above-market operating leases, net 686 1,131 In-place leases 66,526 82,097 Accumulated amortization (36,174 ) (46,625 ) In-place leases, net 30,352 35,472 Below-market ground lease obligation 490 490 Accumulated amortization (54 ) (46 ) Below-market ground lease obligation, net 436 444 Total deferred leasing costs and acquisition-related intangible assets, net $ 197,574 $ 183,728 Acquisition-related Intangible Liabilities, net: (1) Below-market operating leases $ 53,523 $ 65,440 Accumulated amortization (29,978 ) (40,495 ) Below-market operating leases, net 23,545 24,945 Above-market ground lease obligation 6,320 6,320 Accumulated amortization (727 ) (626 ) Above-market ground lease obligation, net 5,593 5,694 Total acquisition-related intangible liabilities, net $ 29,138 $ 30,639 _______________ (1) Included in deferred revenue and acquisition-related intangible liabilities, net in the consolidated balance sheets. The following table sets forth amortization related to deferred leasing costs and acquisition-related intangibles for the years ended December 31, 2018 , 2017 and 2016 . Year Ended December 31, 2018 2017 2016 (in thousands) Deferred leasing costs (1) $ 34,341 $ 31,675 $ 28,639 Above-market operating leases (2) 444 2,240 1,509 In-place leases (1) 15,915 18,650 11,676 Below-market ground lease obligation (3) 8 8 8 Below-market operating leases (4) (10,192 ) (10,768 ) (8,674 ) Above-market ground lease obligation (5) (101 ) (101 ) (101 ) Total $ 40,415 $ 41,704 $ 33,057 _______________ (1) The amortization of deferred leasing costs and in-place leases is recorded to depreciation and amortization expense and the amortization of lease incentives is recorded as a reduction to rental income in the consolidated statements of operations for the periods presented. (2) The amortization of above-market operating leases is recorded as a decrease to rental income in the consolidated statements of operations for the periods presented. (3) The amortization of the below-market ground lease obligation is recorded as an increase to ground lease expense in the consolidated statements of operations for the periods presented. (4) The amortization of below-market operating leases is recorded as an increase to rental income in the consolidated statements of operations for the periods presented. (5) The amortization of the above-market ground lease obligation is recorded as a decrease to ground lease expense in the consolidated statements of operations for the periods presented. The following table sets forth the estimated annual amortization expense related to deferred leasing costs and acquisition-related intangibles as of December 31, 2018 for future periods: Year Deferred Leasing Costs Above-Market Operating Leases (1) In-Place Leases Below-Market Ground Lease Obligation (2) Below-Market Operating Leases (3) Above-Market Ground Lease Obligation (4) (in thousands) 2019 31,980 192 16,675 8 (7,779 ) (100 ) 2020 26,868 38 5,963 8 (4,621 ) (100 ) 2021 21,787 38 2,861 8 (1,938 ) (100 ) 2022 18,683 38 1,589 8 (1,486 ) (100 ) 2023 14,914 38 648 8 (988 ) (100 ) Thereafter 51,868 342 2,616 396 (6,733 ) (5,093 ) Total $ 166,100 $ 686 $ 30,352 $ 436 $ (23,545 ) $ (5,593 ) _______________ (1) Represents estimated annual amortization related to above-market operating leases. Amounts will be recorded as a decrease to rental income in the consolidated statements of operations. (2) Represents estimated annual amortization related to below-market ground lease obligations. Amounts will be recorded as an increase to ground lease expense in the consolidated statements of operations. (3) Represents estimated annual amortization related to below-market operating leases. Amounts will be recorded as an increase to rental income in the consolidated statements of operations. (4) Represents estimated annual amortization related to above-market ground lease obligations. Amounts will be recorded as a decrease to ground lease expense in the consolidated statements of operations.

Receivables

Receivables	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Receivables	Receivables Current Receivables, net Current receivables, net is primarily comprised of contractual rents and other lease-related obligations due from tenants. The balance consisted of the following as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Current receivables $ 24,815 $ 19,235 Allowance for uncollectible tenant receivables (4,639 ) (2,309 ) Current receivables, net $ 20,176 $ 16,926 Deferred Rent Receivables, net Deferred rent receivables, net consisted of the following as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Deferred rent receivables $ 270,346 $ 249,629 Allowance for deferred rent receivables (3,339 ) (3,238 ) Deferred rent receivables, net $ 267,007 $ 246,391 Other Significant Events During the year ended December 31, 2018 , we recognized $5.7 million of provision for bad debts. The provision for bad debts was primarily due to a $7.0 million provision for one tenant recognized during the second quarter of 2018 , partially offset by a $1.4 million decrease in the provision for bad debts for one lease due to the assignment of the lease to a credit tenant during the second quarter of 2018.

Prepaid Expenses and Other Asse

Prepaid Expenses and Other Assets, Net	12 Months Ended
	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Assets, Net	Prepaid Expenses and Other Assets, Net Prepaid expenses and other assets, net consisted of the following at December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Furniture, fixtures and other long-lived assets, net $ 36,833 $ 39,686 Notes receivable (1) 2,113 19,912 Prepaid expenses & acquisition deposits 13,927 55,108 Total Prepaid Expenses and Other Assets, Net $ 52,873 $ 114,706 _______________ (1) During the year ended December 31, 2018 , a note receivable with a balance of $15.1 million was repaid to the Company. Notes receivable are shown net of a valuation allowance of approximately $2.9 million as of December 31, 2018 .

Secured and Unsecured Debt of t

Secured and Unsecured Debt of the Company	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Secured and Unsecured Debt of the Company	Secured and Unsecured Debt of the Company In this Note 8, the “Company” refers solely to Kilroy Realty Corporation and not to any of our subsidiaries. The Company itself does not hold any indebtedness. All of our secured and unsecured debt is held directly by the Operating Partnership. The Company generally guarantees all the Operating Partnership’s unsecured debt obligations including the unsecured revolving credit facility, the $150.0 million unsecured term loan facility and all of the unsecured senior notes. At December 31, 2018 and 2017 , the Operating Partnership had $2.6 billion and $2.0 billion , respectively, outstanding in total, including unamortized discounts and deferred financing costs, under these unsecured debt obligations. In addition, although the remaining $0.3 billion of the Operating Partnership’s debt as of December 31, 2018 and 2017 , is secured and non-recourse to the Company, the Company provides limited customary secured debt guarantees for items such as voluntary bankruptcy, fraud, misapplication of payments and environmental liabilities. Debt Covenants and Restrictions One of the covenants contained within the unsecured revolving credit facility and the unsecured term loan facility as discussed further below in Note 9 prohibits the Company from paying dividends during an event of default in excess of an amount which results in distributions to us in an amount sufficient to permit us to pay dividends to our stockholders that we reasonably believe are necessary to (a) maintain our qualification as a REIT for federal and state income tax purposes and (b) avoid the payment of federal or state income or excise tax.

Secured and Unsecured Debt of_2

Secured and Unsecured Debt of the Operating Partnership	12 Months Ended
	Dec. 31, 2018
Debt Instrument [Line Items]
Secured and Unsecured Debt of the Operating Partnership	Secured and Unsecured Debt of the Company In this Note 8, the “Company” refers solely to Kilroy Realty Corporation and not to any of our subsidiaries. The Company itself does not hold any indebtedness. All of our secured and unsecured debt is held directly by the Operating Partnership. The Company generally guarantees all the Operating Partnership’s unsecured debt obligations including the unsecured revolving credit facility, the $150.0 million unsecured term loan facility and all of the unsecured senior notes. At December 31, 2018 and 2017 , the Operating Partnership had $2.6 billion and $2.0 billion , respectively, outstanding in total, including unamortized discounts and deferred financing costs, under these unsecured debt obligations. In addition, although the remaining $0.3 billion of the Operating Partnership’s debt as of December 31, 2018 and 2017 , is secured and non-recourse to the Company, the Company provides limited customary secured debt guarantees for items such as voluntary bankruptcy, fraud, misapplication of payments and environmental liabilities. Debt Covenants and Restrictions One of the covenants contained within the unsecured revolving credit facility and the unsecured term loan facility as discussed further below in Note 9 prohibits the Company from paying dividends during an event of default in excess of an amount which results in distributions to us in an amount sufficient to permit us to pay dividends to our stockholders that we reasonably believe are necessary to (a) maintain our qualification as a REIT for federal and state income tax purposes and (b) avoid the payment of federal or state income or excise tax.
Kilroy Realty L.P. [Member]
Debt Instrument [Line Items]
Secured and Unsecured Debt of the Operating Partnership	Secured and Unsecured Debt of the Operating Partnership Secured Debt The following table sets forth the composition of our secured debt as of December 31, 2018 and 2017 : Annual Stated Interest Rate (1) GAAP Effective Rate (1)(2) Maturity Date December 31, Type of Debt 2018 2017 (in thousands) Mortgage note payable 3.57% 3.57% December 2026 $ 170,000 $ 170,000 Mortgage note payable (3) 4.48% 4.48% July 2027 91,332 93,081 Mortgage note payable (3)(4) 6.05% 3.50% June 2019 75,238 78,894 Total secured debt $ 336,570 $ 341,975 Unamortized Deferred Financing Costs (1,039 ) (1,175 ) Total secured debt, net $ 335,531 $ 340,800 ______________ (1) All interest rates presented are fixed-rate interest rates. (2) Represents the effective interest rate including the amortization of initial issuance discounts/premiums excluding the amortization of deferred financing costs. (3) The secured debt and the related properties that secure the debt are held in a special purpose entity and the properties are not available to satisfy the debts and other obligations of the Company or the Operating Partnership. (4) As of December 31, 2018 and 2017 , the mortgage loan had unamortized debt premiums of $0.8 million and $2.6 million , respectively. In February 2019, the Company repaid this mortgage note payable at par. The Operating Partnership’s secured debt was collateralized by operating properties with a combined net book value of approximately $324.6 million as of December 31, 2018 . Although our mortgage loans are secured and non-recourse to the Company and the Operating Partnership, the Company provides limited customary secured debt guarantees for items such as voluntary bankruptcy, fraud, misapplication of payments and environmental liabilities. As of December 31, 2018 , all of the Operating Partnership’s secured loans contained restrictions that would require the payment of prepayment penalties for the acceleration of outstanding debt. The mortgage notes payable are secured by deeds of trust on certain of our properties and the assignment of certain rents and leases associated with those properties. Unsecured Senior Notes The following table summarizes the balance and significant terms of the registered unsecured senior notes issued by the Operating Partnership and outstanding, including unamortized discounts of $6.6 million and $6.3 million and unamortized deferred financing costs of $15.4 million and $12.5 million as of December 31, 2018 and 2017 , respectively: Net Carrying Amount Issuance date Maturity date Stated coupon rate Effective interest rate (1) 2018 2017 (in thousands) 4.750% Unsecured Senior Notes (2) November 2018 December 2028 4.750% 4.800% $ 400,000 $ — Unamortized discount and deferred financing costs (4,960 ) — Net carrying amount $ 395,040 $ — 4.350% Unsecured Senior Notes (3) October 2018 October 2026 4.350% 4.350% $ 200,000 $ — Unamortized discount and deferred financing costs (1,375 ) — Net carrying amount $ 198,625 $ — 4.300% Unsecured Senior Notes (3) July 2018 July 2026 4.300% 4.300% $ 50,000 $ — Unamortized discount and deferred financing costs (342 ) — Net carrying amount $ 49,658 $ — 3.450% Unsecured Senior Notes (4) December 2017 December 2024 3.450% 3.470% $ 425,000 $ 425,000 Unamortized discount and deferred financing costs (3,493 ) (4,047 ) Net carrying amount $ 421,507 $ 420,953 3.450% Unsecured Senior Notes (5) February 2017 February 2029 3.450% 3.450% $ 75,000 $ 75,000 Unamortized discount and deferred financing costs (432 ) (475 ) Net carrying amount $ 74,568 $ 74,525 3.350% Unsecured Senior Notes (5) February 2017 February 2027 3.350% 3.350% $ 175,000 $ 175,000 Unamortized discount and deferred financing costs (941 ) (1,056 ) Net carrying amount $ 174,059 $ 173,944 4.375% Unsecured Senior Notes (6) September 2015 October 2025 4.375% 4.444% $ 400,000 $ 400,000 Unamortized discount and deferred financing costs (3,738 ) (4,292 ) Net carrying amount $ 396,262 $ 395,708 4.250% Unsecured Senior Notes (7) July 2014 August 2029 4.250% 4.350% $ 400,000 $ 400,000 Unamortized discount and deferred financing costs (5,632 ) (6,164 ) Net carrying amount $ 394,368 $ 393,836 3.800% Unsecured Senior Notes (8) January 2013 January 2023 3.800% 3.800% $ 300,000 $ 300,000 Unamortized discount and deferred financing costs (1,108 ) (1,382 ) Net carrying amount $ 298,892 $ 298,618 6.625% Unsecured Senior Notes (9) May 2010 June 2020 6.625% 6.744% $ — $ 250,000 Unamortized discount and deferred financing costs — (1,321 ) Net carrying amount $ — $ 248,679 Total Unsecured Senior Notes, Net $ 2,402,979 $ 2,006,263 ________________________ (1) Represents the effective interest rate including the amortization of initial issuance discounts, excluding the amortization of deferred financing costs. (2) Interest on these notes is payable semi-annually in arrears on June 15th and December 15th of each year, beginning on June 15, 2019. (3) Interest on these notes is payable semi-annually in arrears on April 18th and October 18th of each year, beginning in April 18, 2019. (4) Interest on these notes is payable semi-annually in arrears on June 15th and December 15th of each year. (5) Interest on these notes is payable semi-annually in arrears on February 17th and August 17th of each year. (6) Interest on these notes is payable semi-annually in arrears on April 1st and October 1st of each year. (7) Interest on these notes is payable semi-annually in arrears on February 15th and August 15th of each year. (8) Interest on these notes is payable semi-annually in arrears on January 15th and July 15th of each year. (9) Interest on these notes is payable semi-annually in arrears on June 1st and December 1st of each year. Unsecured Senior Notes - Registered Offerings In November 2018, the Operating Partnership issued $400.0 million of aggregate principal amount of unsecured senior notes in a registered public offering, as shown on the table above. The outstanding balance of the unsecured senior notes is included in unsecured debt, net of initial issuance discount of $1.5 million , on our consolidated balance sheets. The unsecured senior notes, which are scheduled to mature on December 15, 2028 , require semi-annual interest payments each June and December based on a stated annual interest rate of 4.750% . The Operating Partnership may redeem the notes at any time prior to December 15, 2028 , either in whole or in part, subject to the payment of an early redemption premium subject to a par call option. In December 2018, we used a portion of the net proceeds from the issuance of our $400.0 million , 4.750% unsecured senior notes to early redeem, at our option, the $250.0 million aggregate principal amount of our outstanding 6.625% unsecured senior notes that were scheduled to mature on June 1, 2020 . In connection with our early redemption, we incurred a $12.6 million loss on early extinguishment of debt comprised of an $11.8 million premium paid to the note holders at the redemption date and a $0.8 million write-off of the unamortized discount and unamortized deferred financing costs. In December 2017, the Operating Partnership issued $425.0 million of aggregate principal amount of unsecured senior notes in a registered public offering, as shown on the table above. The outstanding balance of the unsecured senior notes is included in unsecured debt, net of initial issuance discount of $0.6 million , on our consolidated balance sheet. The unsecured senior notes, which are scheduled to mature on December 15, 2024 , require semi-annual interest payments each June and December based on a stated annual interest rate of 3.450% . The Operating Partnership may redeem the notes at any time prior to September 15, 2024, either in whole or in part, subject to the payment of an early redemption premium. In December 2017, we used a portion of the net proceeds from the issuance of our $425.0 million , 3.450% unsecured senior notes to early redeem, at our option, the $325.0 million aggregate principal amount of our outstanding 4.800% unsecured senior notes that were scheduled to mature on July 15, 2018 . In connection with our early redemption, we incurred a $5.3 million loss on early extinguishment of debt comprised of $5.0 million premium paid to the note holders at the redemption date and $0.3 million write-off of the unamortized discount and unamortized deferred financing costs. Unsecured Senior Notes - Private Placement In May 2018, the Operating Partnership entered into a note purchase agreement in a private placement (the “2018 Note Purchase Agreement”) in connection with the issuance and sale of $50.0 million principal amount of the Operating Partnership’s 4.30% Senior Notes, Series A, due July 18, 2026 (the “Series A Notes due 2026”), and $200.0 million principal amount of the Operating Partnership’s 4.35% Senior Notes, Series B, due October 18, 2026 (the “Series B Notes due 2026” and, together with the Series A Notes, the “Series A and B Notes due 2026”), as shown in the table above. The Company drew the full amount of the Series A Notes due 2026 on July 18, 2018. On October 22, 2018, the Company drew the full amount of the Series B Notes due 2026. The Series A and B Notes due 2026 mature on their respective due dates, unless earlier redeemed or prepaid pursuant to the terms of the 2018 Note Purchase Agreement. Interest on the Series A and B Notes due 2026 is payable semi-annually in arrears on April 18 and October 18 of each year beginning April 18, 2019 . As of December 31, 2018 , there was $50.0 million and $200.0 million issued and outstanding aggregate principal amount of Series A and Series B Notes due 2026, respectively. In September 2016, the Operating Partnership entered into a note purchase agreement in a private placement (the “2016 Note Purchase Agreement”), in connection with the issuance and sale of $175.0 million principal amount of the Operating Partnership’s 3.35% Senior Notes, Series A, due February 17, 2027 (the “Series A Notes due 2027”), and $75.0 million principal amount of the Operating Partnership’s 3.45% Senior Notes, Series B, due February 17, 2029 (the “Series B Notes due 2029” and, together with the Series A Notes due 2027, the “Series A and B Notes due 2027 and 2029”), as shown on the table above. In February 2017, the Operating Partnership issued the $175.0 million principal amount of its Series A Notes due 2027 and the $75.0 million principal amount of its Series B Notes due 2029. The Series A and B Notes due 2027 and 2029 mature on their respective due dates unless earlier redeemed or prepaid pursuant to the terms of the 2016 Note Purchase Agreement. Interest on the Series A and B Notes due 2027 and 2029 is payable semi-annually in arrears on February 17 and August 17 of each year. As of December 31, 2018 , there was $175.0 million and $75.0 million issued and outstanding aggregate principal amount of Series A and B Notes, respectively. The Operating Partnership may, at its option and upon notice to the purchasers of the Series A and B Notes due 2026 and Series A and B Notes due 2027 and 2029, prepay at any time all, or from time to time any part of the principal amounts then outstanding (in an amount not less than 5% of the aggregate principal amount of the Series A and B Notes due 2026 and Series A and B Notes due 2027 and 2029 then outstanding in the case of a partial prepayment), at 100% of the principal amount so prepaid, plus the make-whole amount determined for the prepayment date with respect to such principal amount as set forth in the 2016 & 2018 Note Purchase Agreements. In connection with the issuance of the Series A and B Notes due 2026 and Series A and B Notes due 2027 and 2029, the Company entered into an agreement whereby it will guarantee the payment by the Operating Partnership of all amounts due with respect to the Series A and B Notes due 2026 and Series A and B Notes due 2027 and the performance by the Operating Partnership of its obligations under the 2016 & 2018 Note Purchase Agreements. Unsecured Revolving Credit Facility and Term Loan Facility In July 2017, the Operating Partnership amended and restated the terms of its unsecured revolving credit facility and unsecured term loan facility (together, the “Facility”). The amendment and restatement increased the size of the unsecured revolving credit facility from $600.0 million to $750.0 million , maintained the size of the unsecured term loan facility of $150.0 million , reduced the borrowing costs and extended the maturity date of the Facility to July 2022. The following table summarizes the balance and terms of our unsecured revolving credit facility as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Outstanding borrowings $ 45,000 $ — Remaining borrowing capacity 705,000 750,000 Total borrowing capacity (1) $ 750,000 $ 750,000 Interest rate (2) 3.48 % 2.56 % Facility fee-annual rate (3) 0.200% Maturity date July 2022 _______________ (1) We may elect to borrow, subject to bank approval and obtaining commitments for any additional borrowing capacity, up to an additional $600.0 million under an accordion feature under the terms of the unsecured revolving credit facility and unsecured term loan facility. (2) Our unsecured revolving credit facility interest rate was calculated based on the contractual rate of LIBOR plus 1.000% as of December 31, 2018 and 2017 . (3) Our facility fee is paid on a quarterly basis and is calculated based on the total borrowing capacity. In addition to the facility fee, we incurred debt origination and legal costs. As of December 31, 2018 and 2017 , $4.7 million and $6.0 million of unamortized deferred financing costs, respectively, which are included in prepaid expenses and other assets, net on our consolidated balance sheets, remained to be amortized through the maturity date of our unsecured revolving credit facility. The Company intends to borrow under the unsecured revolving credit facility from time to time for general corporate purposes, to finance development and redevelopment expenditures, to fund potential acquisitions and to potentially repay long-term debt. During the first quarter of 2018, we borrowed the full $150.0 million borrowing capacity of our unsecured term loan facility. In connection with the funding of the outstanding borrowings, we transferred $30.0 million of outstanding borrowings under the unsecured revolving credit facility to the balance of our unsecured term loan facility. As a result, only $120.0 million of cash proceeds were received from the funding of the unsecured term loan facility. The following table summarizes the balance and terms of our unsecured term loan facility as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Outstanding borrowings $ 150,000 $ — Remaining borrowing capacity — 150,000 Total borrowing capacity (1) $ 150,000 $ 150,000 Interest rate (2) 3.49 % 2.66 % Undrawn facility fee-annual rate (3) 0.200% Maturity date July 2022 _______________ (1) As of December 31, 2018 and 2017 , $0.9 million and $1.2 million of unamortized deferred financing costs, respectively, remained to be amortized through the maturity date of our unsecured term loan facility. (2) Our unsecured term loan facility interest rate was calculated based on the contractual rate of LIBOR plus 1.100% as of December 31, 2018 and 2017 . (3) Prior to borrowing the full capacity of our unsecured term loan facility, the undrawn facility fee was calculated based on any unused borrowing capacity and was paid on a quarterly basis. Debt Covenants and Restrictions The unsecured revolving credit facility, the unsecured term loan facility, the unsecured senior notes, the Series A and B Notes due 2026 and Series A and B Notes due 2027 and 2029 and certain other secured debt arrangements contain covenants and restrictions requiring us to meet certain financial ratios and reporting requirements. Some of the more restrictive financial covenants include a maximum ratio of total debt to total asset value, a minimum fixed-charge coverage ratio, a minimum unsecured debt ratio and a minimum unencumbered asset pool debt service coverage ratio. Noncompliance with one or more of the covenants and restrictions could result in the full principal balance of the associated debt becoming immediately due and payable. We believe we were in compliance with all of our debt covenants as of December 31, 2018 and 2017 . Debt Maturities The following table summarizes the stated debt maturities and scheduled amortization payments as of December 31, 2018 : Year (in thousands) 2019 $ 76,309 2020 5,137 2021 5,342 2022 200,554 2023 305,775 Thereafter 2,362,694 Total aggregate principal value (1) $ 2,955,811 ________________________ (1) Includes gross principal balance of outstanding debt before the effect of the following at December 31, 2018 : $17.4 million of unamortized deferred financing costs for the unsecured term loan facility, unsecured senior notes and secured debt, $6.6 million of unamortized discounts for the unsecured senior notes and $0.8 million of unamortized premiums for the secured debt. Capitalized Interest and Loan Fees The following table sets forth gross interest expense, including debt discount/premium and deferred financing cost amortization, net of capitalized interest, for the years ended 2018 , 2017 and 2016 . The interest expense capitalized was recorded as a cost of development and increased the carrying value of undeveloped land and construction in progress. Year Ended December 31, 2018 2017 2016 (in thousands) Gross interest expense $ 117,789 $ 112,577 $ 105,263 Capitalized interest and deferred financing costs (68,068 ) (46,537 ) (49,460 ) Interest expense $ 49,721 $ 66,040 $ 55,803

Deferred Revenue and Acquisitio

Deferred Revenue and Acquisition Related Liabilities, net	12 Months Ended
	Dec. 31, 2018
Deferred Revenue Disclosure [Abstract]
Deferred Revenue and Acquisition Related Liabilities, net	Deferred Revenue and Acquisition-Related Intangible Liabilities, net Deferred revenue and acquisition-related intangible liabilities, net consisted of the following at December 31, 2018 and 2017 : December 31, 2018 2017 (in thousands) Deferred revenue related to tenant-funded tenant improvements $ 104,558 $ 104,260 Other deferred revenue 15,950 10,991 Acquisition-related intangible liabilities, net (1) 29,138 30,639 Total $ 149,646 $ 145,890 ________________________ (1) See Note 5 “Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, net” for additional information regarding our acquisition-related intangible liabilities. Deferred Revenue Related to Tenant-funded Tenant Improvements During the years ended December 31, 2018 , 2017 , and 2016 , $18.4 million , $16.8 million and $13.2 million , respectively, of deferred revenue related to tenant-funded tenant improvements was amortized and recognized as rental income. The following is the estimated amortization of deferred revenue related to tenant-funded tenant improvements as of December 31, 2018 for the next five years and thereafter: Year Ending (in thousands) 2019 $ 16,973 2020 16,265 2021 14,612 2022 13,603 2023 11,857 Thereafter 31,248 Total $ 104,558

Noncontrolling Interests on the

Noncontrolling Interests on the Company's Consolidated Financial Statements	12 Months Ended
	Dec. 31, 2018
Noncontrolling Interest [Abstract]
Noncontrolling Interests on the Company's Consolidated Financial Statements	Noncontrolling Interests on the Company’s Consolidated Financial Statements Common Units of the Operating Partnership The Company owned a 98.0% and 97.9% common general partnership interest in the Operating Partnership as of December 31, 2018 and 2017 , respectively. The remaining 2.0% and 2.1% common limited partnership interest as of December 31, 2018 and 2017 , respectively, was owned by non-affiliated investors and certain of our executive officers and directors in the form of noncontrolling common units. There were 2,025,287 and 2,077,193 common units outstanding held by these investors, executive officers and directors as of December 31, 2018 and 2017 , respectively. The decrease in the common units from December 31, 2017 to December 31, 2018 was attributable to 51,906 common unit redemptions. The noncontrolling common units may be redeemed by unitholders for cash. Except under certain circumstances, we, at our option, may satisfy the cash redemption obligation with shares of the Company’s common stock on a one-for-one basis. If satisfied in cash, the value for each noncontrolling common unit upon redemption is the amount equal to the average of the closing quoted price per share of the Company’s common stock, par value $.01 per share, as reported on the NYSE for the ten trading days immediately preceding the applicable redemption date. The aggregate value upon redemption of the then-outstanding noncontrolling common units was $126.4 million and $154.5 million as of December 31, 2018 and 2017 , respectively. This redemption value does not necessarily represent the amount that would be distributed with respect to each noncontrolling common unit in the event of our termination or liquidation. In the event of our termination or liquidation, it is expected in most cases that each common unit would be entitled to a liquidating distribution equal to the liquidating distribution payable in respect of each share of the Company’s common stock. Noncontrolling Interest in Consolidated Property Partnerships On August 30, 2016, the Operating Partnership entered into agreements with Norges Bank Real Estate Management (“NBREM”) whereby NBREM invested, through two REIT subsidiaries, in two existing companies that owned the Company’s 100 First Street and 303 Second Street office properties located in San Francisco, California. Based on a gross valuation of the properties of approximately $1.2 billion , NBREM contributed a total of $452.9 million , for a 44% common equity interest in the companies, which was net of approximately $55.3 million of its proportionate share of the existing mortgage debt on 303 Second Street as of the transaction date. In November 2017, NBREM contributed $54.4 million to fund their proportionate share of the Company’s repayment of this mortgage debt. The transaction was structured with a staggered closing. On August 30, 2016, the first tranche of the transaction closed and NBREM contributed $191.4 million plus a working capital contribution of $2.1 million for a 44% common ownership interest in 100 First LLC. On November 30, 2016, the second tranche of the transaction closed and NBREM contributed $261.5 million , which was net of its proportionate share of the existing mortgage debt secured by the 303 Second Street property of approximately $55.3 million , plus a working capital contribution of $2.9 million for a 44% common ownership interest in 303 Second LLC. The transactions did not meet the criteria to qualify as sales of real estate because the Company continues to effectively control the properties and therefore continued to account for the 100 First Street and 303 Second Street office properties on a consolidated basis in its financial statements. At formation, the Company accounted for the transactions as equity transactions and recognized noncontrolling interests in its consolidated balance sheets. In connection with the transaction, the Company provides customary property management, leasing and construction management services for both properties. 100 First Street is a 467,095 square foot office tower, and 303 Second Street is a 740,047 square foot office property, both located in the South of Market submarket in San Francisco, California. The noncontrolling interests in 100 First LLC and 303 Second LLC as of December 31, 2018 and 2017 were $186.4 million and $175.4 million , respectively, which is recognized in noncontrolling interests in consolidated property partnerships on the Company’s consolidated balance sheets. The remaining amount of noncontrolling interests in consolidated property partnerships represents the third party equity interest in Redwood LLC. This noncontrolling interest was $6.0 million and $6.2 million as of December 31, 2018 and 2017 , respectively. Noncontrolling Interests on the Operating Partnership’s Consolidated Financial Statements Consolidated Property Partnerships On August 30, 2016, the Operating Partnership entered into agreements with NBREM whereby NBREM invested, through two REIT subsidiaries, in two existing companies that owned the Company’s 100 First Street and 303 Second Street office properties located in San Francisco, California. Based on a gross valuation of the two properties of approximately $1.2 billion , NBREM contributed a total of $452.9 million for a 44% common equity interest in the companies, which is net of approximately $55.3 million of its proportionate share of the existing mortgage debt. In November 2017, the Company repaid the mortgage debt secured by the 303 Second Street office property. Prior to the repayment, NBREM contributed $54.4 million to fund their proportionate share of the repayment. Refer to Note 11 for additional information regarding these transactions.

Noncontrolling Interests on t_2

Noncontrolling Interests on the Operating Partnership's Consolidated Financial Statements	12 Months Ended
	Dec. 31, 2018
Noncontrolling Interest [Abstract]
Noncontrolling Interests on the Operating Partnership’s Consolidated Financial Statements	Noncontrolling Interests on the Company’s Consolidated Financial Statements Common Units of the Operating Partnership The Company owned a 98.0% and 97.9% common general partnership interest in the Operating Partnership as of December 31, 2018 and 2017 , respectively. The remaining 2.0% and 2.1% common limited partnership interest as of December 31, 2018 and 2017 , respectively, was owned by non-affiliated investors and certain of our executive officers and directors in the form of noncontrolling common units. There were 2,025,287 and 2,077,193 common units outstanding held by these investors, executive officers and directors as of December 31, 2018 and 2017 , respectively. The decrease in the common units from December 31, 2017 to December 31, 2018 was attributable to 51,906 common unit redemptions. The noncontrolling common units may be redeemed by unitholders for cash. Except under certain circumstances, we, at our option, may satisfy the cash redemption obligation with shares of the Company’s common stock on a one-for-one basis. If satisfied in cash, the value for each noncontrolling common unit upon redemption is the amount equal to the average of the closing quoted price per share of the Company’s common stock, par value $.01 per share, as reported on the NYSE for the ten trading days immediately preceding the applicable redemption date. The aggregate value upon redemption of the then-outstanding noncontrolling common units was $126.4 million and $154.5 million as of December 31, 2018 and 2017 , respectively. This redemption value does not necessarily represent the amount that would be distributed with respect to each noncontrolling common unit in the event of our termination or liquidation. In the event of our termination or liquidation, it is expected in most cases that each common unit would be entitled to a liquidating distribution equal to the liquidating distribution payable in respect of each share of the Company’s common stock. Noncontrolling Interest in Consolidated Property Partnerships On August 30, 2016, the Operating Partnership entered into agreements with Norges Bank Real Estate Management (“NBREM”) whereby NBREM invested, through two REIT subsidiaries, in two existing companies that owned the Company’s 100 First Street and 303 Second Street office properties located in San Francisco, California. Based on a gross valuation of the properties of approximately $1.2 billion , NBREM contributed a total of $452.9 million , for a 44% common equity interest in the companies, which was net of approximately $55.3 million of its proportionate share of the existing mortgage debt on 303 Second Street as of the transaction date. In November 2017, NBREM contributed $54.4 million to fund their proportionate share of the Company’s repayment of this mortgage debt. The transaction was structured with a staggered closing. On August 30, 2016, the first tranche of the transaction closed and NBREM contributed $191.4 million plus a working capital contribution of $2.1 million for a 44% common ownership interest in 100 First LLC. On November 30, 2016, the second tranche of the transaction closed and NBREM contributed $261.5 million , which was net of its proportionate share of the existing mortgage debt secured by the 303 Second Street property of approximately $55.3 million , plus a working capital contribution of $2.9 million for a 44% common ownership interest in 303 Second LLC. The transactions did not meet the criteria to qualify as sales of real estate because the Company continues to effectively control the properties and therefore continued to account for the 100 First Street and 303 Second Street office properties on a consolidated basis in its financial statements. At formation, the Company accounted for the transactions as equity transactions and recognized noncontrolling interests in its consolidated balance sheets. In connection with the transaction, the Company provides customary property management, leasing and construction management services for both properties. 100 First Street is a 467,095 square foot office tower, and 303 Second Street is a 740,047 square foot office property, both located in the South of Market submarket in San Francisco, California. The noncontrolling interests in 100 First LLC and 303 Second LLC as of December 31, 2018 and 2017 were $186.4 million and $175.4 million , respectively, which is recognized in noncontrolling interests in consolidated property partnerships on the Company’s consolidated balance sheets. The remaining amount of noncontrolling interests in consolidated property partnerships represents the third party equity interest in Redwood LLC. This noncontrolling interest was $6.0 million and $6.2 million as of December 31, 2018 and 2017 , respectively. Noncontrolling Interests on the Operating Partnership’s Consolidated Financial Statements Consolidated Property Partnerships On August 30, 2016, the Operating Partnership entered into agreements with NBREM whereby NBREM invested, through two REIT subsidiaries, in two existing companies that owned the Company’s 100 First Street and 303 Second Street office properties located in San Francisco, California. Based on a gross valuation of the two properties of approximately $1.2 billion , NBREM contributed a total of $452.9 million for a 44% common equity interest in the companies, which is net of approximately $55.3 million of its proportionate share of the existing mortgage debt. In November 2017, the Company repaid the mortgage debt secured by the 303 Second Street office property. Prior to the repayment, NBREM contributed $54.4 million to fund their proportionate share of the repayment. Refer to Note 11 for additional information regarding these transactions.

Stockholders' Equity of the Com

Stockholders' Equity of the Company	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity of the Company	Stockholders’ Equity of the Company Preferred Stock On August 15, 2017 , the Company redeemed all 4,000,000 shares of its 6.375% Series H Cumulative Redeemable Preferred Stock (“Series H Preferred Stock”). The shares of Series H Preferred Stock were redeemed at a redemption price equal to their stated liquidation preference of $25.00 per share, representing $100.0 million in aggregate. The redemption payment did not include any additional accrued dividends because the redemption date was also the dividend payment date. On March 30, 2017 (the “Series G Redemption Date”), the Company redeemed all 4,000,000 shares of its 6.875% Series G Cumulative Redeemable Preferred Stock (“Series G Preferred Stock”). The shares of Series G Preferred Stock were redeemed at a redemption price equal to their stated liquidation preference of $25.00 per share, representing $100.0 million in aggregate, plus all accrued and unpaid dividends to the Series G Redemption Date. In connection with the redemption of the Series G and Series H Preferred Stock, during the year ended December 31, 2017 we recorded non-cash charges of $7.6 million as a reduction to net income available to common stockholders for the original issuance costs of the Series H and Series G Preferred Stock. Common Stock Forward Equity Offering On August 8, 2018, the Company entered into forward equity sale agreements with certain financial institutions acting as forward purchasers in connection with an offering of 5,000,000 shares of common stock at an initial gross offering price of $360.5 million , or $72.10 per share, before underwriting discounts, commissions and offering expenses. The forward purchasers borrowed and sold an aggregate of 5,000,000 shares of common stock in the offering. The Company did not receive any proceeds from the sale of its shares of common stock by the forward purchasers at the time of the offering. The Company currently expects to fully physically settle the forward sale agreements and receive cash proceeds upon one or more settlement dates, at the Company’s discretion, prior to the final settlement date under the forward sale agreements of August 1, 2019. The forward sale price that we expect to receive upon physical settlement of the agreements, which was initially $71.68 per share, will be subject to adjustment for (i) a floating interest rate factor equal to a specified daily rate less a spread, (ii) the forward purchasers’ stock borrowing costs and (iii) scheduled dividends during the term of the forward equity sale agreements. The full amount of this offering remains available for future settlement as of the date of this filing. Upon issuance of shares, the Company will contribute the net proceeds from these issuances to the Operating Partnership in exchange for an equal number of units in the Operating Partnership. Common Stock Issuances In January 2017, the Company completed an underwritten public offering of 4,427,500 shares of its common stock. The net offering proceeds, after deducting underwriting discounts and offering expenses, were approximately $308.8 million . We used a portion of the proceeds to partially fund our $1.90 per share of special dividends declared by our Board of Directors in December 2016 and used the remaining proceeds for general corporate uses, to fund development expenditures and to repay outstanding indebtedness. At-The-Market Stock Offering Program Under our at-the-market stock offering programs, which commenced in December 2014 and June 2018 we may offer and sell shares of our common stock from time to time in “at-the-market” offerings. During the year ended December 31, 2018 , the Company completed its existing at-the-market stock offering program (the “2014 At-The-Market Program”) under which we sold an aggregate of $300.0 million in gross sales of shares, and in June 2018 commenced a new at-the-market stock offering program (the “2018 At-The-Market Program”) under which we may offer and sell shares of our common stock with an aggregate gross sales price of up to $500.0 million . In connection with the 2018 At-The-Market-Program, the Company may, at its discretion, enter into forward equity sale agreements. The use of a forward equity sale agreements would allow the Company to lock in a share price on the sale of shares of our common stock at the time the agreement is executed, but defer receiving the proceeds from the sale of shares until a later date, allowing the Company to better align such funding with its capital needs. The following table sets forth information regarding sales of our common stock under our at-the-market offering programs for the years ended December 31, 2018 , 2017 and 2016 : Year Ended December 31, 2018 2017 2016 (in millions, except share data) Shares of common stock sold during the period 1,817,195 235,077 451,398 Weighted average price per share of common stock $ 73.64 $ 75.40 $ 71.50 Aggregate gross proceeds $ 133.8 $ 17.7 $ 32.3 Aggregate net proceeds after selling commissions $ 132.1 $ 17.5 $ 31.9 The proceeds from sales were used to fund acquisitions, development expenditures and general corporate purposes including repayment of borrowings under the unsecured revolving credit facility. During the year ended December 31, 2018 , under the 2014 At-The-Market Program, we sold 1,369,729 shares of common stock and completed the program. Since commencement of the 2018 At-The-Market Program through December 31, 2018 , we have sold 447,466 shares of common stock, none of which were sold under forward equity sale agreements. Approximately $466.2 million remains available to be sold under this program. Actual future sales will depend upon a variety of factors, including, but not limited to, market conditions, the trading price of the Company’s common stock and our capital needs. We have no obligation to sell the remaining shares available for sale under the 2018 At-The-Market program. Common Stock Repurchases On February 23, 2016, the Company’s Board of Directors approved a 4,000,000 share increase to the Company’s existing share repurchase program bringing the total current repurchase authorization to 4,988,025 shares. The Company did not repurchase shares of common stock under this program during the years ended December 31, 2018 or December 31, 2017 . In March 2016, the Company repurchased 52,199 shares of common stock at a weighted average price of $55.45 per share of common stock for $2.9 million . As of December 31, 2018 , 4,935,826 shares remain eligible for repurchase under the Company’s share repurchase program. Accrued Dividends and Distributions The following tables summarize accrued dividends and distributions for the noted outstanding shares of common stock and noncontrolling units as of December 31, 2018 and 2017 : December 31, 2018 2017 (in thousands) Dividends and Distributions payable to: Common stockholders $ 45,840 $ 41,914 Noncontrolling common unitholders of the Operating Partnership 922 883 RSU holders (1) 797 651 Total accrued dividends and distribution to common stockholders and noncontrolling unitholders $ 47,559 $ 43,448 ______________________ (1) The amount includes the value of the dividend equivalents that will be paid with additional RSUs (see Note 15 “Share-Based Compensation” for additional information). December 31, 2018 2017 Outstanding Shares and Units: Common stock (1) 100,746,988 98,620,333 Noncontrolling common units 2,025,287 2,077,193 RSUs (2) 1,711,628 1,488,724 ______________________ (1) The amount includes nonvested shares. (2) The amount includes nonvested RSUs. Does not include 1,018,337 and 665,110 market measure-based RSUs because not all the necessary performance conditions have been met as of December 31, 2018 and 2017 , respectively. Refer to Note 15 “Share-Based Compensation” for additional information.

Partners' Capital of the Operat

Partners' Capital of the Operating Partnership	12 Months Ended
	Dec. 31, 2018
Partners' Capital [Abstract]
Partners' Capital of the Operating Partnership	Partners' Capital of the Operating Partnership Preferred Units On August 15, 2017 , the Company redeemed all 4,000,000 shares of its 6.375% Series H Preferred Stock. For each share of Series H Preferred Stock that was outstanding, the Company had an equivalent number of 6.375% Series H Preferred Units (“Series H Preferred Units”) outstanding with substantially similar terms as the Series H Preferred Stock. In connection with the redemption of the Series H Preferred Stock, the Series H Preferred Units held by the Company were redeemed by the Operating Partnership. On March 30, 2017 , the Company redeemed all 4,000,000 shares of its 6.875% Series G Preferred Stock. For each share of Series G Preferred Stock that was outstanding, the Company had an equivalent number of 6.875% Series G Preferred Units (“Series G Preferred Units”) outstanding with substantially similar terms as the Series G Preferred Stock. In connection with the redemption of the Series G Preferred Stock, the Series G Preferred Units held by the Company were redeemed by the Operating Partnership. In connection with the redemption of the Series G and Series H Preferred Stock, during the year ended December 31, 2017 we recorded non-cash charges of $7.6 million as a reduction to net income available to common unitholders for the original issuance costs of the Series H and Series G Preferred Stock. Common Units Issuance of Common Units In January 2017, the Company completed an underwritten public offering of 4,427,500 shares of its common stock (see Note 13 “Stockholders’ Equity of the Company”). The net offering proceeds of approximately $308.8 million were contributed by the Company to the Operating Partnership in exchange for 4,427,500 common units. In March 2016, the Operating Partnership issued 867,701 common units in connection with a development acquisition. Each common unit was valued at $55.36 , which was based on a trailing ten-day average of the closing quoted price per share of the Company’s common stock, par value $.01 per share, as reported on the NYSE, as calculated in accordance with the Partnership Agreement. At-The-Market Stock Offering Program During the years ended December 31, 2018 , 2017 and 2016 , the Company utilized its at-the-market stock offering programs to issue shares of common stock (see Note 13 “Stockholders’ Equity of the Company” for additional information). The net offering proceeds and property acquired using net offering proceeds contributed by the Company to the Operating Partnership in exchange for common units for the years ended December 31, 2018 , 2017 and 2016 are as follows: Year Ended December 31, 2018 2017 2016 (in millions, except share and per share data) Shares of common stock contributed by the Company 1,817,195 235,077 451,398 Common units exchanged for shares of common stock by the Company 1,817,195 235,077 451,398 Aggregate gross proceeds $ 133.8 $ 17.7 $ 32.3 Aggregate net proceeds after selling commissions $ 132.1 $ 17.5 $ 31.9 Common Units Outstanding The following table sets forth the number of common units held by the Company and the number of common units held by non-affiliated investors and certain of our executive officers and directors in the form of noncontrolling common units as well as the ownership interest held on each respective date: December 31, 2018 December 31, 2017 Company owned common units in the Operating Partnership 100,746,988 98,620,333 Company owned general partnership interest 98.0 % 97.9 % Noncontrolling common units of the Operating Partnership 2,025,287 2,077,193 Ownership interest of noncontrolling interest 2.0 % 2.1 % For a further discussion of the noncontrolling common units during the years ended December 31, 2018 and 2017 , refer to Note 11 “Noncontrolling Interests on the Company’s Consolidated Financial Statements.” Accrued Distributions The following tables summarize accrued distributions for the noted common units as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Distributions payable to: General partner $ 45,840 $ 41,914 Common limited partners 922 883 RSU holders (1) 797 651 Total accrued distributions to common unitholders $ 47,559 $ 43,448 ______________________ (1) The amount includes the value of the dividend equivalents that will be paid with additional RSUs (see Note 15 “Share-Based Compensation” for additional information). December 31, 2018 December 31, 2017 Outstanding Units: Common units held by the general partner 100,746,988 98,620,333 Common units held by the limited partners 2,025,287 2,077,193 RSUs (1) 1,711,628 1,488,724 ______________________ (1) Does not include 1,018,337 and 665,110 market measure-based RSUs because not all the necessary performance conditions have been met as of December 31, 2018 and 2017 , respectively. Refer to Note 15 “Share-Based Compensation” for additional information.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	hare-Based and Other Compensation Stockholder Approved Share-Based Incentive Compensation Plan As of December 31, 2018 , we maintained one share-based incentive compensation plan, the Kilroy Realty 2006 Incentive Award Plan, as amended (the “2006 Plan”). The Company has a currently effective registration statement registering 9.2 million shares of our common stock for possible issuance under our 2006 Incentive Award Plan. As of December 31, 2018 , approximately 0.6 million shares were available for grant under the 2006 Plan. The calculation of shares available for grant is presented after taking into account a reserve for a sufficient number of shares to cover the vesting and payment of 2006 Plan awards that were outstanding on that date, including performance-based vesting awards at (i) levels actually achieved for the performance conditions (as defined below) for which the performance period has been completed and (ii) at maximum levels for the other performance and market conditions (as defined below) for awards still in a performance period. The Executive Compensation Committee (the “Compensation Committee”) of the Company's Board of Directors may grant the following share-based awards to eligible individuals, as provided under the 2006 Plan: incentive stock options, nonqualified stock options, restricted stock (nonvested shares), stock appreciation rights, performance shares, performance stock units, dividend equivalents, stock payments, deferred stock, restricted stock units (“RSUs”), profit interest units, performance bonus awards, performance-based awards and other incentive awards. For each award granted under our share-based incentive compensation programs, the Operating Partnership simultaneously issues to the Company a number of common units equal to the number of shares of common stock ultimately paid by the Company in respect of such awards. 2018, 2017 and 2016 Share-Based Compensation Grants In connection with entering into an amended employment agreement (the “Amended Employment Agreement”), on December 27, 2018, the Compensation Committee of the Company’s Board of Directors awarded John Kilroy, the Chairman of the Board of Directors, Chief Executive Officer and President of the Company and the Operating Partnership 483,871 RSUs, providing an additional retention incentive during the term of the agreement and enticing Mr. Kilroy to delay his retirement. Of these RSUs awarded, 266,130 RSUs (at the target level of performance) are subject to market-based vesting requirements and 217,741 RSUs are subject to time-based vesting requirements. In addition to Mr. Kilroy’s award, the Compensation Committee of the Company’s Board of Directors awarded 161,290 RSUs to certain members of management. Of these RSUs awarded, 80,647 RSUs (at the target level of performance) are subject to market-based vesting requirements (together totaling 346,777 target RSUs with Mr. Kilroy’s award, the “December 2018 Market-Based RSUs”) and 80,643 RSUs are subject to time-based vesting requirements (together totaling 298,384 RSUs with Mr. Kilroy’s award, the “December 2018 Time-Based RSUs”). In January and February 2018 , the Executive Compensation Committee of the Company’s Board of Directors awarded 282,038 RSUs to certain officers of the Company under the 2006 Plan, which included 158,205 RSUs (at the target level of performance) that are subject to market and/or performance-based vesting requirements (the “2018 Performance-Based RSUs”) and 123,833 RSUs that are subject to time-based vesting requirements (the “2018 Time-Based RSUs”). Additionally, during 2018, 14,999 RSUs were granted to the board of directors and certain members of management subject to time vesting requirements. In February 2017 , the Executive Compensation Committee of the Company’s Board of Directors awarded 229,976 RSUs to certain officers of the Company under the 2006 Plan, which included 130,956 RSUs (at the target level of performance) that are subject to time-based, market-measure based and performance-based vesting requirements (the “2017 Performance-Based RSUs”) and 99,020 RSUs that are subject to time-based vesting requirements (the “2017 Time-Based RSUs”). Additionally, during 2017, 43,081 RSUs were granted to the board of directors and certain members of management subject to time vesting requirements. On January 28, 2016 , the Executive Compensation Committee of the Company’s Board of Directors awarded 294,821 RSUs to certain officers of the Company under the 2006 Plan, which included 168,077 RSUs (at the target level of performance) that are subject to time-based, market-measure based and performance-based vesting requirements (the “2016 Performance-Based RSUs”) and 126,744 RSUs that are subject to time-based vesting requirements (“2016 Time-Based RSUs”). Additionally, during 2016, 47,003 RSUs were granted to the board of directors and certain members of management subject to time vesting requirements. December 2018 Market-Based RSU Grant Between 0% and 200% of the total 346,777 target number of December 2018 Market-Based RSUs will be eligible to vest based on the Company’s relative total shareholder return (“TSR”) versus a comparative group of companies that consist of companies in the SNL US REIT Office Index over the performance period. An initial number of RSUs (the “Initial Number of RSUs”) will be determined at the end of 2021 based on a three -year performance period (2019 through 2021). Once the Initial Number of RSUs is determined, 75% of the Initial Number of RSUs will be scheduled to vest on January 5, 2022. The remaining 25% of the Initial Number of RSUs will be scheduled to vest on January 5, 2023, subject to adjustment based on the Company’s relative TSR for the entire four-year performance period (2019 through 2022). The December 2018 Market-Based RSUs are also subject to service vesting requirements through the scheduled vest dates. Each December 2018 Market-Based RSU represents the right to receive one share of our common stock in the future, subject to, and as modified by, the Company’s level of achievement of the applicable market conditions. The December 27, 2018 grant date fair value of the December 2018 Market-Based RSUs was $23.8 million . The fair value was calculated using a Monte Carlo simulation pricing model based on the assumptions in the table below. For the year ended December 31, 2018 , we recorded compensation expense based upon the $68.66 grant date fair value per share. Compensation expense for the December 2018 Market-Based RSUs is recognized using a graded vesting approach, where 75% of the fair value will be recognized on a straight-line basis over the three-year initial performance period through the end of 2021, and the remaining 25% of the fair value will be recognized on a straight-line basis over the four-year final performance period through the end of 2022. The following table summarizes the assumptions utilized in the Monte Carlo simulation pricing models: December 2018 Market-Based RSU Award Fair Value Assumptions Valuation date December 27, 2018 Fair value per share on valuation date $68.66 Expected share price volatility 23.0% Risk-free interest rate 2.4% The computation of expected volatility was based on a blend of the historical volatility of our shares of common stock over a period of twice the performance period and implied volatility data based on the observed pricing of six month publicly-traded options on shares of our common stock. The risk-free interest rate was based on the yield curve on zero-coupon U.S. Treasury STRIP securities in effect at December 27, 2018. 2018, 2017 and 2016 Annual Performance-Based RSU Grants The 2018 Performance-Based RSUs are scheduled to vest at the end of a three -year period (consisting of calendar years 2018-2020). A target number of 2018 Performance-Based RSUs were awarded, and the final number of 2018 Performance-Based RSUs that vest (which may be more or less than the target number) will be based upon (1) the achievement of pre-set FFO per share goals for the year ending December 31, 2018 that applies to 100% of the Performance-Based RSUs awarded (the “2018 FFO Performance Condition”) and (2) a performance measure that applies to 50% of the award based upon a measure of the Company’s average debt to EBITDA ratio for the three -year performance period (the “2018 Debt to EBITDA Ratio Performance Condition” and together with the 2018 FFO Performance Condition, the “2018 Performance Conditions”) and a market measure that applies to the other 50% of the award based upon the relative ranking of the Company’s TSR for the three -year performance period compared to the TSR of an established comparison group of companies over the same period (the “2018 Market Condition”). The 2018 Performance-Based RSUs are also subject to a three -year service vesting provision and are scheduled to cliff vest on the date the final vesting percentage is determined following the end of the three -year performance period under the awards. The 2018 FFO Performance Condition was achieved 175% of target for one participant and 150% of target for all other participants. The number of 2018 Performance-Based RSUs ultimately earned could fluctuate from the current estimated number of 2018 Performance-Based RSUs granted based upon the levels of achievement for the 2018 Debt to EBITDA Ratio Performance Condition, the 2018 Market Condition and the extent to which the service vesting condition is satisfied. The 2017 Performance-Based RSUs are scheduled to cliff vest at the end of a three -year period (consisting of calendar years 2017-2019) based upon (1) the achievement of pre-defined FFO per share goals for the year ended December 31, 2017 that applies to 100% of the 2017 Performance-Based RSUs awarded (the “2017 FFO Performance Condition”) and (2) also based upon either the average FAD per share growth that applies to 30% of the award or the Company’s average debt to EBITDA ratio that applies to a separate 30% of the award (together, the “Other 2017 Performance Conditions” and together with the 2017 FFO Performance Condition, the “2017 Performance Conditions”) or the relative TSR versus a comparative group of companies that consist of companies in the SNL US REIT Office Index that applies to the remaining 40% of the award (the “2017 Market Condition”) for the three -year period ending December 31, 2019. The 2017 FFO Performance Condition was achieved at a weighted average of approximately 131% of target for the 2017 Performance-Based RSUs. The number of 2017 Performance-Based RSUs ultimately earned could fluctuate from the current estimated number of 2017 Performance-Based RSUs granted based upon the levels of achievement for the Other 2017 Performance Conditions, the 2017 Market Condition and the extent to which the service vesting condition is satisfied. The 2016 Performance-Based RSUs are also scheduled to cliff vest at the end of a three -year service period based upon the achievement of pre-defined FFO per share goals for the year ended December 31, 2016 (the “2016 Performance Condition”) and also upon the average annual relative total stockholder return versus a comparative group of companies that consist of companies in the SNL US REIT Office Index (the “2016 Market Condition”) for the three -year period ending December 31, 2018. Based upon the combined results of the final 2016 Performance Condition and 2016 Market Condition, the 2016 Performance-Based RSUs achieved 144% of their target level of performance. As of December 31, 2018 , the estimated number of RSUs earned for the 2018 and 2017 Performance-Based RSUs and the actual number of RSUs earned for the 2016 Performance-Based RSUs was as follows: 2018 Performance-Based RSUs 2017 Performance-Based RSUs 2016 Performance-Based RSUs Service vesting period February 14, 2018 - January, 2021 February 24, 2017 - January, 2020 January 28, 2016 - January, 2019 Target RSUs granted 158,205 130,956 168,077 Estimated RSUs earned (1) 254,235 170,994 241,438 Date of valuation February 14, 2018 February 24, 2017 January 28, 2016 _______________ (1) Estimated RSUs earned for the 2018 Performance-Based RSUs are based on the actual achievement of the 2018 FFO Performance Condition and assumes target level achievement of the 2018 Debt to EBITDA Ratio Performance Condition and the 2018 Market Condition. Estimated RSUs earned for the 2017 Performance-Based RSUs are based on the actual achievement of the 2017 FFO Performance Condition and assume target level achievement of the 2017 Market Condition and Other 2017 Performance Conditions. The 2016 Performance-Based RSUs earned are based on actual performance of the 2016 Performance Condition and the 2016 Market Condition. Each Performance-Based RSU represents the right to receive one share of our common stock in the future, subject to, and as modified by, the Company’s level of achievement of the applicable performance and market conditions. The fair values of the 2018 Performance-Based RSUs, 2017 Performance-Based RSUs and 2016 Performance-Based RSUs were $10.8 million at February 14, 2018 , $10.3 million at February 24, 2017 and $9.6 million at January 28, 2016 , respectively. The fair values for the awards with market conditions were calculated using a Monte Carlo simulation pricing model based on the assumptions in the table below. The determination of the fair value of the 2018, 2017 and 2016 Performance-Based RSUs takes into consideration the likelihood of achievement of the 2018, 2017 and 2016 Performance Conditions and the 2018, 2017 and 2016 Market Conditions, respectively, as discussed above. The following table summarizes the assumptions utilized in the Monte Carlo simulation pricing models: 2018 Award Fair Value Assumptions 2017 Award Fair Value Assumptions 2016 Award Fair Value Assumptions Valuation date February 14, 2018 February 24, 2017 January 28, 2016 Fair value per share on valuation date $70.08 $80.89 $57.08 Expected share price volatility 20.00% 21.00% 26.00% Risk-free interest rate 2.37% 1.39% 1.13% The computation of expected volatility was based on a blend of the historical volatility of our shares of common stock over a period of twice the remaining performance period as of the grant date and implied volatility data based on the observed pricing of six month publicly-traded options on shares of our common stock. The risk-free interest rate was based on the yield curve on zero-coupon U.S. Treasury STRIP securities in effect at February 14, 2018 , February 24, 2017 and January 28, 2016 . Compensation expense for the Performance-Based RSUs is recognized on a straight-line basis over the requisite service period for each participant, which is generally the three-year service period. However, for one participant there was a shorter service period for their 2017 and 2018 Performance-Based RSUs. As of December 31, 2018 , the number of 2018 Performance-Based RSUs estimated to be earned based on the Company’s estimate of the performance conditions measured against the applicable goals was 254,235 , and the compensation cost recorded to date for this program was based on that estimate. For the portion of the 2018 Performance-Based RSUs subject to the 2018 Market Condition, for the year ended December 31, 2018 , we recorded compensation expense based upon the $70.08 fair value per share at February 14, 2018 . Compensation expense will be variable for the portion of the 2018 Performance-Based RSUs subject to the 2018 Debt to EBITDA Ratio Performance Condition, based upon the outcome of that condition. As of December 31, 2018 , the number of 2017 Performance-Based RSUs estimated to be earned based on the Company’s estimate of the performance conditions measured against the applicable goals was 170,994 , and the compensation cost recorded to date for this program was based on that estimate. For the portion of the 2017 Performance-Based RSUs subject to the 2017 Market Condition, for the years ended December 31, 2018 and 2017 , we recorded compensation expense based upon the $80.89 fair value per share at February 24, 2017 . Compensation expense will be variable for the portion of the 2017 Performance-Based RSUs subject to the Other 2017 Performance Conditions, based upon the outcome of those conditions. For the years ended December 31, 2018 , 2017 and 2016 , we recorded compensation expense for the 2016 Performance-Based RSUs based upon $57.08 fair value per share at January 28, 2016 multiplied by the 241,438 RSUs, which is net of forfeitures, estimated to be earned at December 31, 2016. December 2018 and Annual 2018, 2017 and 2016 Time-Based RSU Grants The annual 2018, 2017 and 2016 Time-Based RSUs are scheduled to vest in equal installments over the periods listed below. The December 2018 Time-Based RSUs are scheduled to vest 50% on January 5, 2022 and 50% on January 5, 2023. Compensation expense for the December 2018 and annual 2018, 2017 and 2016 Time-Based RSUs is recognized on a straight-line basis over the requisite service period, which is generally the explicit service period. However, for one participant there was a shorter service period for their 2017 and 2018 Time-Based RSUs. Each Time-Based RSU represents the right to receive one share of our common stock in the future, subject to continued employment through the applicable vesting date. The total fair value of the Time-Based RSUs is based on the Company's closing share price on the NYSE on the respective fair valuation dates as detailed in the table below: December 2018 Time-Based RSU Grant 2018 Time-Based RSU Grant (1) 2017 Time-Based RSU Grant (2) 2016 Time-Based RSU Grant Service vesting period December 27, 2018 - January 5, 2023 January & February 2018 - January 5, 2021 February 2017 - January 5, 2020 January 28, 2016 - January 5, 2019 Fair value on valuation date (in millions) $ 18.5 $ 8.4 $ 7.5 $ 7.1 Fair value per share $ 62.00 $ 70.37 $ 73.30 $ 56.23 Date of fair valuation December 27, 2018 January & February 2018 February 2017 January 28, 2016 _______________ (1) The 2018 Time-Based RSUs consist of 56,015 RSUs granted on January 29, 2018 at a fair value per share of $70.37 and 67,818 RSUs granted on February 14, 2018 at a fair value per share of $66.46 . (2) The 2017 Time-Based RSUs consist of 41,119 RSUs granted on February 3, 2017 at a fair value per share of $73.30 and 57,901 RSUs granted on February 24, 2017 at a fair value per share of $77.16 . Summary of Performance and Market-Measure Based RSUs A summary of our performance and market-measure based RSU activity from January 1, 2018 through December 31, 2018 is presented below: Nonvested RSUs Vested RSUs Total RSUs Amount Weighted-Average (1) Outstanding at January 1, 2018 665,110 $ 68.83 55,672 720,782 Granted 601,012 68.51 1,067 602,079 Vested (261,875 ) 74.25 261,875 — Settled (2) (285,818 ) (285,818 ) Issuance of dividend equivalents (3) 14,090 71.75 2,976 17,066 Forfeited — (11 ) (11 ) Outstanding as of December 31, 2018 (4) 1,018,337 $ 67.29 35,761 1,054,098 _______________ (1) Represents the grant-date fair value for all awards, excluding the 2014 Performance-Based RSU Grant, which was re-measured upon stockholder approval of the amended 2006 Plan on May 22, 2014, as an insufficient number of shares were available to settle these RSUs upon initial grant on January 29, 2014. (2) Represents vested RSUs that were settled in shares of the Company’s common stock. Total shares settled include 139,933 shares that were tendered in accordance with the terms of the 2006 Plan to satisfy minimum statutory tax withholding requirements related to the RSUs settled. We accept the return of RSUs at the current quoted closing share price of the Company’s common stock to satisfy tax obligations. (3) Represents the issuance of dividend equivalents earned on the underlying RSUs. The dividend equivalents vest based on terms specified under the related RSU award agreement. (4) Outstanding RSUs as of December 31, 2018 represent the actual achievement of the FFO performance conditions and assumes target levels for the market and other performance conditions. The number of restricted stock units ultimately earned is subject to change based upon actual performance over the three-year vesting period. Dividend equivalents earned will vest along with the underlying award and are also subject to changes based on the number of RSUs ultimately earned for each underlying award. A summary of our performance and market-measure based RSU activity for years ended December 31, 2018 , 2017 and 2016 is presented below: RSUs Granted RSUs Vested Years ended December 31, Non-Vested RSUs Granted (1) Weighted-Average Fair Value Per Share (2) Vested RSUs Total Vest-Date Fair Value (in thousands) 2018 601,012 $ 68.51 (265,918 ) $ 18,906 2017 170,994 78.97 (194,991 ) 14,270 2016 258,393 57.36 (36,914 ) 2,788 _______________ (1) Non-vested RSUs granted during the years ended December 31, 2018 and 2017 are based on the actual achievement of the FFO performance conditions and assumes target level achievement for the market and other performance conditions. Non-vested RSUs granted during the year ended December 31, 2016 are based on the final performance of both the 2016 Performance and Market Conditions, and are non-vested as of December 31, 2018 as they were subject to the Compensation Committee’s confirmation of final performance. (2) Represents the grant-date fair value for all awards, excluding the 2014 Performance-Based RSU Grant, which was re-measured upon stockholder approval of the amended 2006 Plan on May 22, 2014, as an insufficient number of shares were available to settle these RSUs upon initial grant on January 29, 2014. Summary of Time-Based RSUs A summary of our time-based RSU activity from January 1, 2018 through December 31, 2018 is presented below: Nonvested RSUs Vested RSUs Total RSUs Amount Weighted Average Fair Value (1) Outstanding at January 1, 2018 331,546 $ 66.83 1,080,928 1,412,474 Granted 437,216 64.21 — 437,216 Vested (187,209 ) 63.85 187,209 — Settled (2) (202,536 ) (202,536 ) Issuance of dividend equivalents (3) 6,316 71.75 26,922 33,238 Forfeited (1,090 ) 70.62 — (1,090 ) Canceled (4) (3,435 ) (3,435 ) Outstanding as of December 31, 2018 586,779 $ 65.87 1,089,088 1,675,867 _______________ (1) Represents the grant-date fair value for all awards, excluding the 2014 Performance-Based RSU Grant, which was re-measured upon stockholder approval of the amended 2006 Plan on May 22, 2014, as an insufficient number of shares were available to settle these RSUs upon initial grant on January 29, 2014. (2) Represents vested RSUs that were settled in shares of the Company’s common stock. Total shares settled include 85,598 shares that were tendered in accordance with the terms of the 2006 Plan to satisfy minimum statutory tax withholding requirements related to the RSUs settled. We accept the return of RSUs at the current quoted closing share price of the Company’s common stock to satisfy tax obligations. (3) Represents the issuance of dividend equivalents earned on the underlying RSUs. The dividend equivalents vest based on terms specified under the related RSU award agreement. (4) For shares vested but not yet settled, we accept the return of RSUs at the current quoted closing share price of the Company’s common stock to satisfy minimum statutory tax-withholding requirements related to either the settlement or vesting of RSUs in accordance with the terms of the 2006 Plan. A summary of our time-based RSU activity for the years ended December 31, 2018 , 2017 and 2016 is presented below: RSUs Granted RSUs Vested Year ended December 31, Non-Vested RSUs Issued Weighted-Average Grant Date Fair Value Per Share Vested RSUs Total Vest-Date Fair Value (1) (in thousands) 2018 437,216 $ 64.21 (214,131 ) $ 14,768 2017 142,101 74.91 (228,095 ) 16,735 2016 173,747 58.29 (130,784 ) 8,438 _______________ (1) Total fair value of RSUs vested was calculated based on the quoted closing share price of the Company’s common stock on the NYSE on the day of vesting. Excludes the issuance of dividend equivalents earned on the underlying RSUs. The dividend equivalents vest based on terms specified under the related RSU award agreement. Summary of Nonvested Restricted Stock A summary of our nonvested restricted stock activity from January 1, 2018 through December 31, 2018 is presented below: Nonvested Weighted-Average Outstanding at January 1, 2018 22,884 $ 55.23 Transferred from time-based RSUs — — Vested (1) (22,884 ) 55.23 Outstanding as of December 31, 2018 — $ — _______________ (1) The total shares vested includes 9,637 shares that were tendered in accordance with the terms of the 2006 Plan to satisfy minimum statutory tax withholding requirements related to the restricted shares that have vested. We accept the return of shares at the current quoted closing share price of the Company’s common stock to satisfy tax withholding obligations. A summary of our nonvested and vested restricted stock activity for years ended December 31, 2018 , 2017 and 2016 is presented below: Shares Granted Shares Vested Years ended December 31, Nonvested Shares Issued Weighted-Average Grant Date Fair Value Per Share Vested Shares Total Fair Value at Vest Date (1) (in thousands) 2018 — $ — (22,884 ) $ 1,652 2017 — — (24,261 ) 1,781 2016 — — (24,262 ) 1,527 _______________ (1) Total fair value of shares vested was calculated based on the quoted closing share price of the Company’s common stock on the NYSE on the date of vesting. Share-Based Compensation Cost Recorded During the Period The total compensation cost for all share-based compensation programs was $35.9 million , $26.3 million and $26.6 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Of the total share-based compensation costs, $8.0 million , $7.3 million and $5.6 million was capitalized as part of real estate assets and deferred leasing costs for the years ended December 31, 2018 , 2017 and 2016 , respectively. As of December 31, 2018 , there was approximately $60.5 million of total unrecognized compensation cost related to nonvested incentive awards granted under share-based compensation arrangements that is expected to be recognized over a weighted-average period of 3.0 years. The remaining compensation cost related to these nonvested incentive awards had been recognized in periods prior to December 31, 2018 . The $60.5 million of unrecognized compensation costs does not reflect the future compensation cost related to share-based awards that were granted subsequent to December 31, 2018 . Other Compensation On December 27, 2018, the Executive Compensation Committee of the Company’s Board approved, and the Company and the Operating Partnership entered into the Amended Employment Agreement with John Kilroy, which amends and supersedes the existing employment agreement dated January 1, 2012. Except as noted below, the Amended Employment Agreement continues Mr. Kilroy’s employment on terms substantially similar to those of the existing employment agreement, with a new term scheduled to continue through December 31, 2023. The Amended Employment Agreement includes a cash retirement benefit of $13.2 million , or $16.2 million for a retirement at or after attaining age 73 , with at least twelve months’ advance notice or at or after the end of the term of the agreement. For the year ended December 31, 2018, the Company recognized $12.1 million of compensation expense in general and administrative expenses on the consolidated statement of operations, representing the present value of the potential cash retirement benefit amount that was earned based on prior service.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans 401(k) Plan We have a retirement savings plan designed to qualify under Section 401(k) of the Code (the “401(k) Plan”). Our employees are eligible to participate in the 401(k) Plan on the first day of the month after three months of service. The 401(k) Plan allows eligible employees (“401(k) Participants”) to defer up to 60% of their eligible compensation on a pre-tax basis, subject to certain maximum amounts allowed by the Code. The 401(k) Plan provides for a matching contribution by the Company in an amount equal to 50 cents of each one dollar of participant contributions up to a maximum of 10% of the 401(k) Participant’s annual salary. 401(k) Participants vest immediately in the amounts contributed by us. For each of the years ended December 31, 2018 , 2017 , and 2016 , we contributed $1.5 million , $1.3 million and $1.2 million , respectively, to the 401(k) Plan. Deferred Compensation Plan In 2007, we adopted the Deferred Compensation Plan, under which directors and certain management employees may defer receipt of their compensation, including up to 70% of their salaries and up to 100% of their director fees and bonuses, as applicable. In addition, employee participants will receive mandatory Company contributions to their Deferred Compensation Plan accounts equal to 10% of their gross monthly salaries, without regard to whether such employees elect to defer salary or bonus compensation under the Deferred Compensation Plan. Our Board may, but has no obligation to, approve additional discretionary contributions by the Company to Participant accounts. We hold the Deferred Compensation Plan assets in a limited rabbi trust, which is subject to the claims of our creditors in the event of bankruptcy or insolvency. See Note 19 “Fair Value Measurements and Disclosures” for further discussion of our Deferred Compensation Plan assets as of December 31, 2018 and 2017 . Our liability of $21.7 million and $20.6 million under the Deferred Compensation Plan was fully funded as of December 31, 2018 and 2017 , respectively.

Future Minimum Rent

Future Minimum Rent	12 Months Ended
	Dec. 31, 2018
Leases [Abstract]
Future Minimum Rent	Future Minimum Rent We have operating leases with tenants that expire at various dates through 2043 and are either subject to scheduled fixed increases or adjustments in rent based on the Consumer Price Index. Generally, the leases grant tenants renewal options. Leases also provide for additional rents based on certain operating expenses. Future contractual minimum rent under operating leases as of December 31, 2018 for future periods is summarized as follows: Year Ending (in thousands) 2019 $ 566,783 2020 632,875 2021 631,835 2022 620,684 2023 586,371 Thereafter 3,240,143 Total (1) $ 6,278,691 ______________ (1) Excludes residential leases and leases with a term of one year or less.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies General As of December 31, 2018 , we had commitments of approximately $960.1 million , excluding our ground lease commitments, for contracts and executed leases directly related to our operating and development properties. Ground Leases The following table summarizes our properties that are held subject to long-term noncancellable ground lease obligations and the respective contractual expiration dates: Property Contractual Expiration Date (1) 601 108th Ave NE, Bellevue, WA November 2093 701, 801 and 837 N. 34th Street, Seattle, WA (2) December 2041 1701 Page Mill Road and 3150 Porter Drive, Palo Alto, CA December 2067 Kilroy Airport Center Phases I, II, and III, Long Beach, CA July 2084 ____________________ (1) Reflects the contractual expiration date prior to the impact of any extension or purchase options held by the Company. (2) The Company has three 10 -year and one 45 -year extension options for this ground lease, which if exercised would extend the expiration date to December 2116. The minimum commitment under our ground leases as of December 31, 2018 for five years and thereafter is as follows: Year Ending (in thousands) 2019 $ 5,154 2020 5,154 2021 5,154 2022 5,154 2023 5,154 Thereafter 233,619 Total (1)(2)(3)(4)(5) $ 259,389 ________________________ (1) Excludes contingent future rent payments based on gross income or adjusted gross income and reflects the minimum ground lease obligations before the impact of ground lease extension options. (2) One of our ground lease obligations is subject to a fair market value adjustment every five years ; however, the lease includes ground rent subprotection and infrastructure rent credits which currently limit our annual rental obligations to $1.0 million . The contractual obligations for that ground lease included above assumes the lesser of $1.0 million or annual lease rental obligation in effect as of December 31, 2018 . (3) One of our ground lease obligations includes a component which is based on the percentage of gross income that exceeds the minimum ground rent. The minimum rent is subject to increases every five years based on 50% of the average annual percentage rent for the previous five years. The contractual obligations for that lease included above assume the current annual ground lease obligation in effect at December 31, 2018 for the remainder of the lease term since we cannot predict future adjustments. (4) One of our ground lease obligations is subject to a fair market value adjustment every five years based on a combination of CPI adjustments and third-party appraisals limited to maximum increases annually. The contractual obligations for that lease included above assume the current annual ground lease obligation in effect at December 31, 2018 for the remainder of the lease term since we cannot predict future adjustments. (5) One of our ground lease obligations includes a component which is based on the percentage of adjusted gross income that exceeds the minimum ground rent. The minimum rent is subject to increases every 10 years by an amount equal to 60% of the average annual percentage rent for the previous three years. The contractual obligations for this lease included above assume the current annual ground lease obligation in effect at December 31, 2018 for the remainder of the lease term since we cannot predict future adjustments. Environmental Matters We follow the policy of monitoring all of our properties, including acquisition, development, and existing stabilized portfolio properties, for the presence of hazardous or toxic substances. While there can be no assurance that a material environmental liability does not exist, we are not currently aware of any environmental liability with respect to our stabilized portfolio properties that would have a material adverse effect on our financial condition, results of operations and cash flow, or that we believe would require additional disclosure or the recording of a loss contingency. As of December 31, 2018 and 2017 , we had accrued environmental remediation liabilities of approximately $83.2 million and $28.3 million , respectively, recorded on our consolidated balance sheets in connection with certain of our in-process and future development projects. The accrued environmental remediation liabilities represent the remaining costs we estimate we will incur prior to and during the development process at various development acquisition sites. These estimates, which we developed with the assistance of third party experts, consist primarily of the removal of contaminated soil, performing environmental closure activities, constructing remedial systems, and other related costs since we are required to dispose of any existing contaminated soil, and sometimes perform other environmental closure or remedial activities, when we develop new buildings at these sites. We record estimated environmental remediation obligations for acquired properties at the acquisition date when we are aware of such costs and when such costs are probable of being incurred and can be reasonably estimated. Estimated costs related to development environmental remediation liabilities are recorded as an increase to the cost of the development project. Actual costs are recorded as a decrease to the liability when incurred. These accruals are adjusted as an increase or decrease to the development project costs and as an increase or decrease to the accrued environmental remediation liability if we obtain further information or circumstances change. The environmental remediation obligations recorded at December 31, 2018 and 2017 were not discounted to their present values since the amount and timing of cash payments are not fixed. It is possible that we could incur additional environmental remediation costs in connection with these development projects. However, potential additional environmental costs for these development projects cannot be reasonably estimated at this time and certain changes in estimates could occur as the site conditions, final project timing, design elements, actual soil conditions and other aspects of the projects, which may depend upon municipal and other approvals beyond the control of the Company, are determined. Other than the accrued environmental liabilities discussed above, we are not aware of any unasserted claims and assessments with respect to an environmental liability that we believe would require additional disclosure or the recording of an additional loss contingency. Litigation We and our properties are subject to litigation arising in the ordinary course of business. To our knowledge, neither we nor any of our properties are presently subject to any litigation or threat of litigation which, if determined unfavorably to us, would have a material adverse effect on our cash flow, financial condition, or results of operations. Insurance We maintain commercial general liability, auto liability, employers’ liability, umbrella/excess liability, special form property, difference in conditions including earthquake and flood, environmental, rental loss, and terrorism insurance covering all of our properties. Management believes the policy specifications and insured limits are reasonable given the relative risk of loss, the cost of the coverage, and industry practice. We do not carry insurance for generally uninsurable losses such as loss from governmental action, nuclear hazard, and war and military action. Policies are subject to various terms, conditions, and exclusions and some policies may involve large deductibles or co-payments. Property Damage Settlement During the year ended December 31, 2016 , we settled an outstanding property damage matter and received cash proceeds totaling $5.0 million , which is included in other property income on our consolidated statements of operations.

Fair Value Measurements and Dis

Fair Value Measurements and Disclosures	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements and Disclosures	Fair Value Measurements and Disclosures Assets and Liabilities Reported at Fair Value The only assets we record at fair value on our consolidated financial statements are the marketable securities related to our Deferred Compensation Plan (see Note 16 “Employee Benefit Plans” for additional information). The following table sets forth the fair value of our marketable securities as of December 31, 2018 and 2017 : Fair Value (Level 1) (1) 2018 2017 Description (in thousands) Marketable securities (2) $ 21,779 $ 20,674 _______________ (1) Based on quoted prices in active markets for identical securities. (2) The marketable securities are held in a limited rabbi trust . We report the change in the fair value of the marketable securities at the end of each accounting period in interest income and other net investment (losses) gains in the consolidated statements of operations. We also adjust the related Deferred Compensation Plan liability to fair value at the end of each accounting period based on the performance of the benchmark funds selected by each participant, which results in a corresponding increase or decrease to compensation cost for the period. The following table sets forth the net (loss) gain on marketable securities recorded during the years ended December 31, 2018 , 2017 and 2016 : December 31, 2018 2017 2016 Description (in thousands) Net (loss) gain on marketable securities $ (1,851 ) $ 3,023 $ 1,130 Financial Instruments Disclosed at Fair Value The following table sets forth the carrying value and the fair value of our other financial instruments as of December 31, 2018 and 2017 : December 31, 2018 2017 Carrying Value Fair Value (1) Carrying Value Fair Value (1) (in thousands) Liabilities Secured debt, net $ 335,531 $ 335,885 $ 340,800 $ 346,858 Unsecured debt, net 2,552,070 2,546,386 2,006,263 2,077,199 Unsecured line of credit (1) 45,000 45,058 — — _______________ (1) Fair value calculated using Level II inputs, which are based on model-derived valuations in which significant inputs and significant value drivers are observable in active markets.

Other Significant Events

Other Significant Events	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Other Significant Events	Receivables Current Receivables, net Current receivables, net is primarily comprised of contractual rents and other lease-related obligations due from tenants. The balance consisted of the following as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Current receivables $ 24,815 $ 19,235 Allowance for uncollectible tenant receivables (4,639 ) (2,309 ) Current receivables, net $ 20,176 $ 16,926 Deferred Rent Receivables, net Deferred rent receivables, net consisted of the following as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Deferred rent receivables $ 270,346 $ 249,629 Allowance for deferred rent receivables (3,339 ) (3,238 ) Deferred rent receivables, net $ 267,007 $ 246,391 Other Significant Events During the year ended December 31, 2018 , we recognized $5.7 million of provision for bad debts. The provision for bad debts was primarily due to a $7.0 million provision for one tenant recognized during the second quarter of 2018 , partially offset by a $1.4 million decrease in the provision for bad debts for one lease due to the assignment of the lease to a credit tenant during the second quarter of 2018.

Net Income Available to Common

Net Income Available to Common Stockholders Per Share of the Company	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Income Available to Common Stockholders Per Share of the Company	Net Income Available to Common Stockholders Per Share of the Company The following table reconciles the numerator and denominator in computing the Company’s basic and diluted per-share computations for net income available to common stockholders for the years ended December 31, 2018 , 2017 and 2016 : Year Ended December 31, 2018 2017 2016 (in thousands, except unit and per unit amounts) Numerator: Net income attributable to Kilroy Realty Corporation $ 258,415 $ 164,612 $ 293,788 Total preferred dividends — (13,363 ) (13,250 ) Allocation to participating securities (1) (2,004 ) (1,975 ) (3,839 ) Numerator for basic and diluted net income available to common stockholders $ 256,411 $ 149,274 $ 276,699 Denominator: Basic weighted average vested shares outstanding 99,972,359 98,113,561 92,342,483 Effect of dilutive securities 510,006 613,770 680,551 Diluted weighted average vested shares and common stock equivalents outstanding 100,482,365 98,727,331 93,023,034 Basic earnings per share: Net income available to common stockholders per share $ 2.56 $ 1.52 $ 3.00 Diluted earnings per share: Net income available to common stockholders per share $ 2.55 $ 1.51 $ 2.97 ________________________ (1) Participating securities include nonvested shares, certain time-based RSUs and vested market measure-based RSUs. Share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are considered participating securities. The impact of potentially dilutive common shares, including stock options, RSUs, shares issuable under executed forward equity sale agreements and other securities are considered in our diluted earnings per share calculation for the years ended December 31, 2018 , 2017 , and 2016 . Certain market measure-based RSUs are not included in dilutive securities as of December 31, 2018 , 2017 , and 2016 as not all performance metrics had been met by the end of the applicable reporting periods. See Note 15 “Share-Based Compensation” for additional information regarding the stock options and other share-based compensation.

Net Income Available to Commo_2

Net Income Available to Common Unitholders Per Unit of the Operating Partnership	12 Months Ended
	Dec. 31, 2018
Kilroy Realty L.P. [Member]
Net Income Available To Common Unitholders [Line Items]
Net Income Available to Common Unitholders per Unit of the Operating Partnership	Net Income Available to Common Unitholders Per Unit of the Operating Partnership The following table reconciles the numerator and denominator in computing the Operating Partnership’s basic and diluted per-unit computations for net income available to common unitholders for the years ended 2018 , 2017 and 2016 : Year Ended December 31, 2018 2017 2016 (in thousands, except unit and per unit amounts) Numerator: Net income attributable to Kilroy Realty, L.P. $ 263,210 $ 167,440 $ 300,063 Total preferred distributions — (13,363 ) (13,250 ) Allocation to participating securities (1) (2,004 ) (1,975 ) (3,839 ) Numerator for basic and diluted net income available to common unitholders $ 261,206 $ 152,102 $ 282,974 Denominator: Basic weighted average vested units outstanding 102,025,276 100,246,567 94,771,688 Effect of dilutive securities 510,006 613,770 680,551 Diluted weighted average vested units and common unit equivalents outstanding 102,535,282 100,860,337 95,452,239 Basic earnings per unit: Net income available to common unitholders per unit $ 2.56 $ 1.52 $ 2.99 Diluted earnings per unit: Net income available to common unitholders per unit $ 2.55 $ 1.51 $ 2.96 ________________________ (1) Participating securities include nonvested shares, certain time-based RSUs and vested market measure-based RSUs. Share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are considered participating securities. The impact of potentially dilutive common units, including stock options, RSUs, shares issuable under executed forward equity sale agreements and other securities are considered in our diluted earnings per share calculation for the years ended December 31, 2018 , 2017 and 2016 . Certain market measure-based RSUs are not included in dilutive securities as of December 31, 2018 , 2017 and 2016 as not all performance metrics had been met by the end of the applicable reporting periods. See Note 15 “Share-Based Compensation” for additional information regarding the stock options and other share-based compensation.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information of the Company	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information of the Company	Supplemental Cash Flow Information of the Company Supplemental cash flow information follows (in thousands): Year Ended December 31, 2018 2017 2016 SUPPLEMENTAL CASH FLOWS INFORMATION: Cash paid for interest, net of capitalized interest of $65,627, $44,757, and $47,675 as of December 31, 2018, 2017 and 2016, respectively $ 44,697 $ 67,336 $ 54,295 NON-CASH INVESTING TRANSACTIONS: Accrual for expenditures for operating properties and development and redevelopment properties $ 158,626 $ 116,089 $ 62,589 Tenant improvements funded directly by tenants $ 13,968 $ 15,314 $ 18,050 Assumption of other assets and liabilities in connection with operating and development property acquisitions, net (Note 3) $ 40,624 $ 1,443 $ 5,863 Accrual for receivable related to development properties $ — $ — $ 1,350 NON-CASH FINANCING TRANSACTIONS: Accrual of dividends and distributions payable to common stockholders and common unitholders (Notes 13 and 28) $ 47,559 $ 43,448 $ 220,650 Exchange of common units of the Operating Partnership into shares of the Company’s common stock $ 1,962 $ 10,939 $ 8,893 Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders (Note 13) $ — $ — $ 1,656 Issuance of common units of the Operating Partnership in connection with an acquisition $ — $ — $ 48,033 Secured debt assumed by buyers in connection with land disposition (Note 4) $ — $ — $ 2,322 The following is a reconciliation of our cash and cash equivalents and restricted cash at the beginning and end of the years ended 2018 , 2017 and 2016 . Year Ended December 31, 2018 2017 2016 RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH: Cash and cash equivalents at beginning of period $ 57,649 $ 193,418 $ 56,508 Restricted cash at beginning of period 9,149 56,711 696 Cash and cash equivalents and restricted cash at beginning of period $ 66,798 $ 250,129 $ 57,204 Cash and cash equivalents at end of period $ 51,604 $ 57,649 $ 193,418 Restricted cash at end of period 119,430 9,149 56,711 Cash and cash equivalents and restricted cash at end of period $ 171,034 $ 66,798 $ 250,129 Supplemental Cash Flow Information of the Operating Partnership: Supplemental cash flow information follows (in thousands): Year Ended December 31, 2018 2017 2016 SUPPLEMENTAL CASH FLOWS INFORMATION: Cash paid for interest, net of capitalized interest of $65,627, $44,757, and $47,675 as of December 31, 2018, 2017 and 2016, respectively $ 44,697 $ 67,336 $ 54,295 NON-CASH INVESTING TRANSACTIONS: Accrual for expenditures for operating properties and development and redevelopment properties $ 158,626 $ 116,089 $ 62,589 Tenant improvements funded directly by tenants $ 13,968 $ 15,314 $ 18,050 Assumption of other assets and liabilities in connection with operating and development property acquisitions, net (Note 3) $ 40,624 $ 1,443 $ 5,863 Accrual for receivable related to development properties $ — $ — $ 1,350 NON-CASH FINANCING TRANSACTIONS: Accrual of dividends and distributions payable to common stockholders and common $ 47,559 $ 43,448 $ 220,650 Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders (Note 14) $ — $ — $ 1,656 Issuance of common units in connection with a development property acquisition $ — $ — $ 48,033 Secured debt assumed by buyers in connection with land disposition (Note 4) $ — $ — $ 2,322 The following is a reconciliation of our cash and cash equivalents and restricted cash at the beginning and end of the years ended 2018 , 2017 and 2016 . Year Ended December 31, 2018 2017 2016 RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH: Cash and cash equivalents at beginning of period $ 57,649 $ 193,418 $ 56,508 Restricted cash at beginning of period 9,149 56,711 696 Cash and cash equivalents and restricted cash at beginning of period $ 66,798 $ 250,129 $ 57,204 Cash and cash equivalents at end of period $ 51,604 $ 57,649 $ 193,418 Restricted cash at end of period 119,430 9,149 56,711 Cash and cash equivalents and restricted cash at end of period $ 171,034 $ 66,798 $ 250,129

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information of the Operating Partnership	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information of the Operating Partnership	Supplemental Cash Flow Information of the Company Supplemental cash flow information follows (in thousands): Year Ended December 31, 2018 2017 2016 SUPPLEMENTAL CASH FLOWS INFORMATION: Cash paid for interest, net of capitalized interest of $65,627, $44,757, and $47,675 as of December 31, 2018, 2017 and 2016, respectively $ 44,697 $ 67,336 $ 54,295 NON-CASH INVESTING TRANSACTIONS: Accrual for expenditures for operating properties and development and redevelopment properties $ 158,626 $ 116,089 $ 62,589 Tenant improvements funded directly by tenants $ 13,968 $ 15,314 $ 18,050 Assumption of other assets and liabilities in connection with operating and development property acquisitions, net (Note 3) $ 40,624 $ 1,443 $ 5,863 Accrual for receivable related to development properties $ — $ — $ 1,350 NON-CASH FINANCING TRANSACTIONS: Accrual of dividends and distributions payable to common stockholders and common unitholders (Notes 13 and 28) $ 47,559 $ 43,448 $ 220,650 Exchange of common units of the Operating Partnership into shares of the Company’s common stock $ 1,962 $ 10,939 $ 8,893 Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders (Note 13) $ — $ — $ 1,656 Issuance of common units of the Operating Partnership in connection with an acquisition $ — $ — $ 48,033 Secured debt assumed by buyers in connection with land disposition (Note 4) $ — $ — $ 2,322 The following is a reconciliation of our cash and cash equivalents and restricted cash at the beginning and end of the years ended 2018 , 2017 and 2016 . Year Ended December 31, 2018 2017 2016 RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH: Cash and cash equivalents at beginning of period $ 57,649 $ 193,418 $ 56,508 Restricted cash at beginning of period 9,149 56,711 696 Cash and cash equivalents and restricted cash at beginning of period $ 66,798 $ 250,129 $ 57,204 Cash and cash equivalents at end of period $ 51,604 $ 57,649 $ 193,418 Restricted cash at end of period 119,430 9,149 56,711 Cash and cash equivalents and restricted cash at end of period $ 171,034 $ 66,798 $ 250,129 Supplemental Cash Flow Information of the Operating Partnership: Supplemental cash flow information follows (in thousands): Year Ended December 31, 2018 2017 2016 SUPPLEMENTAL CASH FLOWS INFORMATION: Cash paid for interest, net of capitalized interest of $65,627, $44,757, and $47,675 as of December 31, 2018, 2017 and 2016, respectively $ 44,697 $ 67,336 $ 54,295 NON-CASH INVESTING TRANSACTIONS: Accrual for expenditures for operating properties and development and redevelopment properties $ 158,626 $ 116,089 $ 62,589 Tenant improvements funded directly by tenants $ 13,968 $ 15,314 $ 18,050 Assumption of other assets and liabilities in connection with operating and development property acquisitions, net (Note 3) $ 40,624 $ 1,443 $ 5,863 Accrual for receivable related to development properties $ — $ — $ 1,350 NON-CASH FINANCING TRANSACTIONS: Accrual of dividends and distributions payable to common stockholders and common $ 47,559 $ 43,448 $ 220,650 Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders (Note 14) $ — $ — $ 1,656 Issuance of common units in connection with a development property acquisition $ — $ — $ 48,033 Secured debt assumed by buyers in connection with land disposition (Note 4) $ — $ — $ 2,322 The following is a reconciliation of our cash and cash equivalents and restricted cash at the beginning and end of the years ended 2018 , 2017 and 2016 . Year Ended December 31, 2018 2017 2016 RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH: Cash and cash equivalents at beginning of period $ 57,649 $ 193,418 $ 56,508 Restricted cash at beginning of period 9,149 56,711 696 Cash and cash equivalents and restricted cash at beginning of period $ 66,798 $ 250,129 $ 57,204 Cash and cash equivalents at end of period $ 51,604 $ 57,649 $ 193,418 Restricted cash at end of period 119,430 9,149 56,711 Cash and cash equivalents and restricted cash at end of period $ 171,034 $ 66,798 $ 250,129

Tax Treatment of Distributions

Tax Treatment of Distributions	12 Months Ended
	Dec. 31, 2018
Tax Treatment of Distributions [Abstract]
Tax Treatment of Distributions	Tax Treatment of Distributions The following table reconciles the dividends declared per share of common stock to the dividends paid per share of common stock during the years ended December 31, 2018 , 2017 and 2016 as follows: Year Ended December 31, Dividends 2018 2017 2016 Dividends declared per share of common stock $ 1.790 $ 1.650 $ 3.375 Less: Dividends declared in the current year and paid in the following year (0.455 ) (0.425 ) (2.275 ) Add: Dividends declared in the prior year and paid in the current year (1) 0.425 2.275 0.350 Dividends paid per share of common stock $ 1.760 $ 3.500 $ 1.450 _________________ (1) The fourth quarter 2016 dividend of $2.275 per share of common stock consists of a special cash dividend of $1.90 per share of common stock and a regular quarterly cash dividend of $0.375 per share of common stock. The $1.90 per share special distribution is treated as paid in two tax years for income tax purposes: $1.587 is treated as paid on December 31, 2016 and $0.313 is treated as paid on January 13, 2017. The $0.375 per share regular quarterly distribution is considered a 2017 dividend distribution for income tax purposes. The unaudited income tax treatment for the dividends to common stockholders reportable for the years ended December 31, 2018 , 2017 and 2016 as identified in the table above was as follows: Year Ended December 31, Shares of Common Stock 2018 2017 2016 Ordinary income (1) $ 1.474 83.73 % $ 1.356 70.87 % $ 1.500 49.40 % Qualified dividend 0.003 0.19 0.002 0.11 0.002 0.06 Return of capital 0.275 15.64 0.344 18.00 — — Capital gains (2) 0.008 0.44 — — 1.212 39.89 Unrecaptured section 1250 gains — — 0.211 11.02 0.323 10.65 $ 1.760 100.00 % $ 1.913 100.00 % $ 3.037 100.00 % _________________ (1) The Tax Cuts and Jobs Act enacted on December 22, 2017 generally allows a deduction for noncorporate taxpayers equal to 20% of ordinary dividends distributed by a REIT (excluding capital gain dividends and qualified dividend income). The amount of dividend eligible for this deduction is referred to as the Section 199A Dividend. For the year ended December 31, 2018 , the Section 199A Dividend is equal to the total ordinary income dividend. (2) Capital gains are comprised entirely of 20% rate gains. The 6.875% Series G Cumulative Redeemable Preferred Stock was issued in March 2012 and redeemed in March 2017. The unaudited income tax treatment for the dividends to Series G preferred stockholders reportable for the years ended December 31, 2017 and 2016 was as follows: Year Ended December 31, Preferred Shares 2017 2016 Ordinary income $ 0.371 86.43 % $ 0.848 49.31 % Qualified dividend 0.001 0.14 0.001 0.06 Capital gains (1) — — 0.687 39.97 Unrecaptured section 1250 gains 0.058 13.43 0.183 10.66 $ 0.430 100.00 % $ 1.719 100.00 % __________________ (1) Capital gains are comprised entirely of 20% rate gains. The 6.375% Series H Cumulative Redeemable Preferred Stock was issued in August 2012 and redeemed in August 2017. The unaudited income tax treatment for the dividends to Series H preferred stockholders reportable for the years ended December 31, 2017 and 2016 was as follows: Year Ended December 31, Preferred Shares 2017 2016 Ordinary income $ 1.033 86.43 % $ 0.786 49.31 % Qualified dividend 0.002 0.14 0.001 0.06 Capital gains (1) — — 0.637 39.97 Unrecaptured section 1250 gains 0.160 13.43 0.170 10.66 $ 1.195 100.00 % $ 1.594 100.00 % __________________ (1) Capital gains are comprised entirely of 20% rate gains.

Quarterly Financial Information

Quarterly Financial Information of the Company (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information of the Company (Unaudited)	Quarterly Financial Information of the Company (Unaudited) Summarized quarterly financial data for the years ended December 31, 2018 and 2017 was as follows: 2018 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per share amounts) Revenues $ 182,822 $ 187,072 $ 186,562 $ 190,842 Net income 40,971 31,755 38,310 166,890 Net income attributable to Kilroy Realty Corporation 36,246 27,549 34,400 160,220 Net income available to common stockholders 36,246 27,549 34,400 160,220 Net income available to common stockholders per share – basic 0.36 0.27 0.34 1.59 Net income available to common stockholders per share – diluted 0.36 0.27 0.33 1.58 2017 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per share amounts) Revenues $ 179,308 $ 180,598 $ 181,534 $ 177,561 Net income 37,281 35,306 75,488 32,540 Net income attributable to Kilroy Realty Corporation 33,525 31,448 71,110 28,529 Preferred dividends and distributions (7,196 ) (1,615 ) (4,552 ) — Net income available to common stockholders 26,329 29,833 66,558 28,529 Net income available to common stockholders per share – basic 0.27 0.30 0.67 0.28 Net income available to common stockholders per share – diluted 0.26 0.30 0.67 0.28 ____________________ (1) The summation of the quarterly financial data may not equal the annual number reported on the consolidated statements of operations due to rounding. For the year ended December 31, 2018 , the summation of the quarterly net income available to common stockholders per share does not equal the annual number reported on the consolidated statements of operations due to the Company’s at-the-market stock offering programs that occurred during the year.

Quarterly Financial Informati_2

Quarterly Financial Information of the Operating Partnership (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information of the Operating Partnership (Unaudited)	Quarterly Financial Information of the Company (Unaudited) Summarized quarterly financial data for the years ended December 31, 2018 and 2017 was as follows: 2018 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per share amounts) Revenues $ 182,822 $ 187,072 $ 186,562 $ 190,842 Net income 40,971 31,755 38,310 166,890 Net income attributable to Kilroy Realty Corporation 36,246 27,549 34,400 160,220 Net income available to common stockholders 36,246 27,549 34,400 160,220 Net income available to common stockholders per share – basic 0.36 0.27 0.34 1.59 Net income available to common stockholders per share – diluted 0.36 0.27 0.33 1.58 2017 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per share amounts) Revenues $ 179,308 $ 180,598 $ 181,534 $ 177,561 Net income 37,281 35,306 75,488 32,540 Net income attributable to Kilroy Realty Corporation 33,525 31,448 71,110 28,529 Preferred dividends and distributions (7,196 ) (1,615 ) (4,552 ) — Net income available to common stockholders 26,329 29,833 66,558 28,529 Net income available to common stockholders per share – basic 0.27 0.30 0.67 0.28 Net income available to common stockholders per share – diluted 0.26 0.30 0.67 0.28 ____________________ (1) The summation of the quarterly financial data may not equal the annual number reported on the consolidated statements of operations due to rounding. For the year ended December 31, 2018 , the summation of the quarterly net income available to common stockholders per share does not equal the annual number reported on the consolidated statements of operations due to the Company’s at-the-market stock offering programs that occurred during the year.
Kilroy Realty L.P. [Member]
Quarterly Financial Information of the Operating Partnership (Unaudited)	Quarterly Financial Information of the Operating Partnership (Unaudited) Summarized quarterly financial data for the years ended December 31, 2018 and 2017 was as follows: 2018 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per unit amounts) Revenues $ 182,822 $ 187,072 $ 186,562 $ 190,842 Net income 40,971 31,755 38,310 166,890 Net income attributable to the Operating Partnership 36,893 28,015 34,993 163,309 Net income available to common unitholders 36,893 28,015 34,993 163,309 Net income available to common unitholders per unit – basic 0.36 0.27 0.34 1.58 Net income available to common unitholders per unit – diluted 0.36 0.27 0.33 1.57 2017 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per unit amounts) Revenues $ 179,308 $ 180,598 $ 181,534 $ 177,561 Net income 37,281 35,306 75,488 32,540 Net income attributable to the Operating Partnership 34,054 31,971 72,402 29,013 Preferred distributions (7,196 ) (1,615 ) (4,552 ) — Net income available to common unitholders 26,858 30,356 67,850 29,013 Net income available to common unitholders per unit – basic 0.26 0.30 0.67 0.28 Net income available to common unitholders per unit – diluted 0.26 0.30 0.67 0.28 ___________________ (1) The summation of the quarterly financial data may not equal the annual number reported on the consolidated statements of operations due to rounding. For the year ended December 31, 2018 , the summation of the quarterly net income available to common stockholders per share does not equal the annual number reported on the consolidated statements of operations due to the Company’s at-the-market stock offering programs that occurred during the year.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On January 15, 2019 , $47.5 million of dividends were paid out to common stockholders, common unitholders and RSU holders of record on December 31, 2018 . In February 2019, the Executive Compensation Committee granted 144,982 Time-Based RSUs and 143,396 Performance-Based RSUs to key employees under the 2006 Plan. The compensation cost related to the RSUs is expected to be recognized over a period of three years. On February 11, 2019, the Company repaid at par a secured mortgage note payable due in June 2019 for $74.3 million .

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS Years ended December 31, 2018 , 2017 and 2016 (in thousands) Balance at Beginning of Period Charged to Costs and Expenses (1) Recoveries (Deductions) Balance at End of Period Allowance for Uncollectible Tenant Receivables for the year ended December 31, 2018 – Allowance for uncollectible tenant receivables $ 2,309 $ 2,604 $ (274 ) $ 4,639 2017 – Allowance for uncollectible tenant receivables 1,712 1,517 (920 ) 2,309 2016 – Allowance for uncollectible tenant receivables 2,080 — (368 ) 1,712 Allowance for Deferred Rent Receivables for the year ended December 31, 2018 – Allowance for deferred rent $ 3,238 $ 165 $ (64 ) $ 3,339 2017 – Allowance for deferred rent 1,524 1,752 (38 ) 3,238 2016 – Allowance for deferred rent 1,882 — (358 ) 1,524 __________________ (1) In addition, for the year ended December 31, 2018 , $2.9 million was charged to costs and expenses for a valuation allowance for a note receivable.

Schedule III - Real Estate and

Schedule III - Real Estate and Accumulated Depreciation	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Abstract]
Schedule III - Real Estate and Accumulated Depreciation	SCHEDULE III – REAL ESTATE AND ACCUMULATED DEPRECIATION December 31, 2018 Initial Cost Gross Amounts at Which Carried at Close of Period Property Location Encumb- rances Land and improve- ments Buildings and Improve- ments Costs Capitalized Subsequent to Acquisition/ Improvement Land and improve- ments Buildings and Improve- ments Total Accumulated Depreciation Depreci- ation Life (1) Date of Acquisition (A)/ Construction (C) (2) Rentable Square Feet (3) (unaudited) ($ in thousands) Office Properties: 2829 Townsgate Rd., Thousand Oaks, CA $ 5,248 $ 8,001 $ 8,267 $ 5,248 $ 16,268 $ 21,516 $ 11,862 35 1997 ( A ) 84,098 2240 E. Imperial Highway, El Segundo, CA 1,044 11,763 29,509 1,048 41,268 42,316 25,671 35 1983 ( C ) 122,870 2250 E. Imperial Highway, El Segundo, CA 2,579 29,062 36,148 2,547 65,242 67,789 52,858 35 1983 ( C ) 298,728 2260 E. Imperial Highway, El Segundo, CA 2,518 28,370 36,672 2,547 65,013 67,560 14,064 35 1983 ( C ) 298,728 909 N. Pacific Coast Highway, El Segundo, CA (4) 3,577 34,042 48,056 3,577 82,098 85,675 38,602 35 2005 ( C ) 244,136 999 N. Pacific Coast Highway, El Segundo, CA (4) 1,407 34,326 16,497 1,407 50,823 52,230 23,178 35 2003 ( C ) 128,588 6115 W. Sunset Blvd., Los Angeles, CA (5) 1,313 3 16,458 2,455 15,319 17,774 1,483 35 2015 ( C ) 26,105 6121 W. Sunset Blvd., Los Angeles, CA (5) 11,120 4,256 43,952 8,703 50,625 59,328 5,631 35 2015 ( C ) 91,173 1525 N. Gower Street, Los Angeles, CA (5) 1,318 3 9,642 1,318 9,645 10,963 870 35 2016 ( C ) 9,610 1575 N. Gower Street, Los Angeles, CA (5) 22,153 51 119,406 22,153 119,457 141,610 8,149 35 2016 ( C ) 251,245 1500 N. El Centro Ave., Los Angeles, CA (5) 9,235 21 58,582 9,235 58,603 67,838 4,026 35 2016 ( C ) 104,504 1550 N. El Centro Ave., Los Angeles, CA (5) (6) 16,970 39 135,583 16,970 135,622 152,592 9,911 35 2016 ( C ) — 6255 W. Sunset Blvd., Los Angeles, CA 18,111 60,320 44,535 18,111 104,855 122,966 29,278 35 2012 ( A ) 323,920 3750 Kilroy Airport Way, Long Beach, CA — 1,941 11,153 — 13,094 13,094 10,395 35 1989 ( C ) 10,457 3760 Kilroy Airport Way, Long Beach, CA — 17,467 13,714 — 31,181 31,181 25,635 35 1989 ( C ) 165,278 3780 Kilroy Airport Way, Long Beach, CA — 22,319 23,008 — 45,327 45,327 37,365 35 1989 ( C ) 219,777 3800 Kilroy Airport Way, Long Beach, CA — 19,408 20,838 — 40,246 40,246 23,575 35 2000 ( C ) 192,476 3840 Kilroy Airport Way, Long Beach, CA — 13,586 10,364 — 23,950 23,950 15,417 35 1999 ( C ) 136,026 3880 Kilroy Airport Way, Long Beach, CA — 9,704 11,277 — 20,981 20,981 3,820 35 1997 ( A ) 96,035 3900 Kilroy Airport Way, Long Beach, CA — 12,615 11,983 — 24,598 24,598 17,147 35 1997 ( A ) 129,893 Kilroy Airport Center, Phase IV, Long Beach, CA (7) — — 4,997 — 4,997 4,997 4,997 35 — — — 8560 W. Sunset Blvd, West Hollywood, CA 9,720 50,956 600 9,720 51,556 61,276 4,209 35 2016 ( A ) 71,875 8570 W. Sunset Blvd, West Hollywood, CA 31,693 27,974 925 31,693 28,899 60,592 2,085 35 2016 ( A ) 43,603 8580 W. Sunset Blvd, West Hollywood, CA 10,013 3,695 135 10,013 3,830 13,843 264 35 2016 ( A ) 7,126 8590 W. Sunset Blvd, West Hollywood, CA 39,954 27,884 1,092 39,954 28,976 68,930 2,267 35 2016 ( A ) 56,095 12100 W. Olympic Blvd., Los Angeles, CA 170,000 (8) 352 45,611 18,518 9,633 54,848 64,481 27,316 35 2003 ( C ) 152,048 12200 W. Olympic Blvd., Los Angeles, CA (8) 4,329 35,488 23,707 3,977 59,547 63,524 37,257 35 2000 ( C ) 150,832 12233 W. Olympic Blvd., Los Angeles, CA 22,100 53,170 3,986 22,100 57,156 79,256 11,832 35 2012 ( A ) 151,029 12312 W. Olympic Blvd., Los Angeles, CA (8) 3,325 12,202 11,341 3,399 23,469 26,868 12,017 35 1997 ( A ) 76,644 1633 26th St., Santa Monica, CA 2,080 6,672 3,139 2,040 9,851 11,891 6,908 35 1997 ( A ) 43,857 2100/2110 Colorado Ave., Santa Monica, CA 91,332 (9) 5,474 26,087 14,620 5,476 40,705 46,181 24,031 35 1997 ( A ) 102,864 3130 Wilshire Blvd., Santa Monica, CA 8,921 6,579 15,992 9,188 22,304 31,492 14,674 35 1997 ( A ) 90,074 501 Santa Monica Blvd., Santa Monica, CA (4) 4,547 12,044 14,129 4,551 26,169 30,720 15,614 35 1998 ( A ) 76,803 2211 Michelson, Irvine, CA (9) 9,319 82,836 6,629 9,319 89,465 98,784 27,097 35 2010 ( A ) 271,556 12225 El Camino Real, Del Mar, CA 1,700 9,633 3,493 1,673 13,153 14,826 8,905 35 1998 ( A ) 58,401 KILROY REALTY CORPORATION AND KILROY REALTY, L.P. SCHEDULE III – REAL ESTATE AND ACCUMULATED DEPRECIATION – (Continued) December 31, 2018 Initial Cost Gross Amounts at Which Carried at Close of Period Property Location Encumb- rances Land and improve- ments Buildings and Improve- ments Costs Capitalized Subsequent to Acquisition/ Improvement Land and improve- ments Buildings and Improve- ments Total Accumulated Depreciation Depreci- ation Life (1) Date of Acquisition (A)/ Construction (C) (2) Rentable Square Feet (3) (unaudited) ($ in thousands) 12235 El Camino Real, Del Mar, CA 1,507 8,543 8,965 1,540 17,475 19,015 9,681 35 1998 ( A ) 53,751 12340 El Camino Real, Del Mar, CA 4,201 13,896 9,858 4,201 23,754 27,955 11,257 35 2002 ( C ) 89,272 12390 El Camino Real, Del Mar, CA 3,453 11,981 3,896 3,453 15,877 19,330 8,995 35 2000 ( C ) 70,140 12348 High Bluff Dr., Del Mar, CA 1,629 3,096 6,141 1,629 9,237 10,866 6,206 35 1999 ( C ) 38,806 12400 High Bluff Dr., Del Mar, CA (4) 15,167 40,497 14,337 15,167 54,834 70,001 27,243 35 2004 ( C ) 209,220 3579 Valley Centre Dr., Del Mar, CA 2,167 6,897 7,449 2,858 13,655 16,513 9,512 35 1999 ( C ) 52,418 3611 Valley Centre Dr., Del Mar, CA 4,184 19,352 18,881 5,259 37,158 42,417 24,251 35 2000 ( C ) 129,656 3661 Valley Centre Dr., Del Mar, CA 4,038 21,144 16,178 4,725 36,635 41,360 20,619 35 2001 ( C ) 128,364 3721 Valley Centre Dr., Del Mar, CA 4,297 18,967 14,569 4,254 33,579 37,833 15,893 35 2003 ( C ) 115,193 3811 Valley Centre Dr., Del Mar, CA 3,452 16,152 20,105 4,457 35,252 39,709 21,545 35 2000 ( C ) 112,067 12770 El Camino Real, Del Mar, CA 9,360 — 33,628 9,360 33,628 42,988 1,950 35 2015 ( C ) 73,032 12780 El Camino Real, Del Mar, CA 18,398 54,954 14,775 18,398 69,729 88,127 11,995 35 2013 ( A ) 140,591 12790 El Camino Real, Del Mar, CA 10,252 21,236 1,426 10,252 22,662 32,914 4,794 35 2013 ( A ) 78,836 13280 Evening Creek Dr. South, I-15 Corridor, CA 3,701 8,398 4,730 3,701 13,128 16,829 5,167 35 2008 ( C ) 41,196 13290 Evening Creek Dr. South, I-15 Corridor, CA 5,229 11,871 5,919 5,229 17,790 23,019 5,950 35 2008 ( C ) 61,180 13480 Evening Creek Dr. North, I-15 Corridor, CA 7,997 — 52,143 7,997 52,143 60,140 18,660 35 2008 ( C ) 154,157 13500 Evening Creek Dr. North, I-15 Corridor, CA 7,581 35,903 15,331 7,580 51,235 58,815 20,471 35 2004 ( A ) 137,658 13520 Evening Creek Dr. North, I-15 Corridor, CA 7,581 35,903 15,427 7,580 51,331 58,911 22,819 35 2004 ( A ) 146,701 2305 Historic Decatur Rd., Point Loma, CA 5,240 22,220 7,309 5,240 29,529 34,769 9,248 35 2010 ( A ) 107,456 4690 Executive Dr., University Towne Centre, CA 1,623 7,926 3,668 1,623 11,594 13,217 7,324 35 1999 ( A ) 47,846 4100 Bohannon Dr., Menlo Park, CA (4) 4,835 15,526 525 4,860 16,026 20,886 3,954 35 2012 ( A ) 47,379 4200 Bohannon Dr., Menlo Park, CA (4) 4,798 15,406 3,222 4,662 18,764 23,426 4,915 35 2012 ( A ) 45,451 4300 Bohannon Dr., Menlo Park, CA (4) 6,527 20,958 2,955 6,470 23,970 30,440 6,996 35 2012 ( A ) 63,079 4400 Bohannon Dr., Menlo Park, CA (4) 4,798 15,406 2,943 4,939 18,208 23,147 5,066 35 2012 ( A ) 48,146 4500 Bohannon Dr., Menlo Park, CA (4) 6,527 20,957 2,025 6,470 23,039 29,509 5,665 35 2012 ( A ) 63,078 4600 Bohannon Dr., Menlo Park, CA (4) 4,798 15,406 3,326 4,939 18,591 23,530 4,924 35 2012 ( A ) 48,147 4700 Bohannon Dr., Menlo Park, CA (4) 6,527 20,958 1,422 6,470 22,437 28,907 5,492 35 2012 ( A ) 63,078 1290 - 1300 Terra Bella Ave., Mountain View, CA 28,730 27,555 29 28,730 27,584 56,314 3,589 35 2016 ( A ) 114,175 331 Fairchild Dr., Mountain View, CA (4) 18,396 17,712 7,955 18,396 25,667 44,063 4,674 35 2013 ( C ) 87,147 680 E. Middlefield Rd., Mountain View, CA 34,605 — 56,464 34,605 56,464 91,069 7,908 35 2014 ( C ) 170,090 690 E. Middlefield Rd., Mountain View, CA 34,755 — 56,707 34,755 56,707 91,462 7,942 35 2014 ( C ) 170,823 1701 Page Mill Rd, Palo Alto, CA — 99,522 25 — 99,547 99,547 6,000 35 2016 ( A ) 128,688 3150 Porter Drive, Palo Alto, CA — 21,715 4 — 21,719 21,719 1,591 35 2016 ( A ) 36,897 900 Jefferson Ave., Redwood City, CA (10) 16,668 — 109,313 18,063 107,918 125,981 11,977 35 2015 ( C ) 228,505 900 Middlefield Rd., Redwood City, CA (10) 7,959 — 49,862 8,626 49,195 57,821 5,204 35 2015 ( C ) 118,764 303 Second St., San Francisco, CA (11) 63,550 154,153 70,133 63,550 224,286 287,836 71,553 35 2010 ( A ) 740,047 KILROY REALTY CORPORATION AND KILROY REALTY, L.P. SCHEDULE III – REAL ESTATE AND ACCUMULATED DEPRECIATION – (Continued) December 31, 2018 Initial Cost Gross Amounts at Which Carried at Close of Period Property Location Encumb- rances Land and improve- ments Buildings and Improve- ments Costs Capitalized Subsequent to Acquisition/ Improvement Land and improve- ments Buildings and Improve- ments Total Accumulated Depreciation Depreci- ation Life (1) Date of Acquisition (A)/ Construction (C) (2) Rentable Square Feet (3) (unaudited) ($ in thousands) 100 First St., San Francisco, CA (12) 49,150 131,238 63,503 49,150 194,741 243,891 53,081 35 2010 ( A ) 467,095 250 Brannan St., San Francisco, CA 7,630 22,770 4,466 7,630 27,236 34,866 9,786 35 2011 ( A ) 100,850 201 Third St., San Francisco, CA 19,260 84,018 66,543 19,260 150,561 169,821 46,541 35 2011 ( A ) 346,538 301 Brannan St., San Francisco, CA 5,910 22,450 5,109 5,910 27,559 33,469 8,375 35 2011 ( A ) 82,834 360 Third St., San Francisco, CA — 88,235 112,885 28,504 172,616 201,120 39,931 35 2011 ( A ) 429,796 333 Brannan St., San Francisco, CA 18,645 — 78,426 18,645 78,426 97,071 6,451 35 2016 ( C ) 185,602 350 Mission Street, San Francisco, CA 52,815 — 213,459 52,815 213,459 266,274 17,818 35 2016 ( C ) 455,340 100 Hooper Street, San Francisco, CA (15) 78,564 — 179,739 78,564 179,739 258,303 1,043 1,043 35 0.035 2018 ( C ) — 345 Brannan St., San Francisco, CA 29,405 113,179 — 29,405 113,179 142,584 — — 35 0.035 2018 ( A ) 110,030 345 Oyster Point Blvd., South San Francisco, CA 13,745 18,575 2 13,745 18,577 32,322 611 35 2018 ( A ) 40,410 347 Oyster Point Blvd, South San Francisco, CA 14,071 18,289 8 14,071 18,297 32,368 602 35 2018 ( A ) 39,780 349 Oyster Point Blvd., South San Francisco, CA 23,112 22,601 771 23,112 23,372 46,484 919 35 2018 ( A ) 65,340 505 Mathilda Ave., Sunnyvale, CA 37,843 1,163 50,450 37,943 51,513 89,456 6,388 35 2014 ( C ) 212,322 555 Mathilda Ave., Sunnyvale, CA 37,843 1,163 50,447 37,943 51,510 89,453 6,387 35 2014 ( C ) 212,322 605 Mathilda Ave., Sunnyvale, CA 29,014 891 77,281 29,090 78,096 107,186 14,036 35 2014 ( C ) 162,785 599 Mathilda Ave., Sunnyvale, CA 13,538 12,559 58 13,538 12,617 26,155 3,568 35 2012 ( A ) 76,031 601 108th Ave., Bellevue, WA — 214,095 33,860 — 247,955 247,955 70,018 35 2011 ( A ) 488,470 10900 NE 4th St., Bellevue, WA 25,080 150,877 36,619 25,080 187,496 212,576 46,105 35 2012 ( A ) 428,557 837 N. 34th St., Lake Union, WA — 37,404 3,817 — 41,221 41,221 9,697 35 2012 ( A ) 111,580 701 N. 34th St., Lake Union, WA — 48,027 7,989 — 56,016 56,016 13,785 35 2012 ( A ) 138,994 801 N. 34th St., Lake Union, WA — 58,537 1,657 — 60,194 60,194 14,159 35 2012 ( A ) 169,412 320 Westlake Avenue North, WA 74,479 (13) 14,710 82,018 5,063 14,710 87,081 101,791 16,693 35 2013 ( A ) 184,644 321 Terry Avenue North, Lake Union, WA (13) 10,430 60,003 9,987 10,430 69,990 80,420 13,046 35 2013 ( A ) 135,755 401 Terry Avenue North, Lake Union, WA 22,500 77,046 — 22,500 77,046 99,546 12,888 35 2014 ( A ) 140,605 TOTAL OPERATING PROPERTIES 335,811 1,117,915 2,777,476 2,472,731 1,160,138 5,207,984 6,368,122 1,391,368 13,232,580 Undeveloped land and construction in progress — 940,092 — 1,118,418 940,092 1,118,418 2,058,510 — — TOTAL ALL PROPERTIES $ 335,811 (14) $ 2,058,007 $ 2,777,476 $ 3,591,149 $ 2,100,230 $ 6,326,402 $ 8,426,632 $ 1,391,368 13,232,580 KILROY REALTY CORPORATION AND KILROY REALTY, L.P. SCHEDULE III – REAL ESTATE AND ACCUMULATED DEPRECIATION – (Continued) December 31, 2018 __________________ (1) The initial costs of buildings and improvements are depreciated over 35 years using a straight-line method of accounting; improvements capitalized subsequent to acquisition are depreciated over the shorter of the lease term or useful life, generally ranging from one to 20 years. (2) Represents our date of construction or acquisition, or of our predecessor, the Kilroy Group. (3) Includes square footage from our stabilized portfolio. (4) These properties secure intercompany promissory notes between KRLP and consolidated property partnerships. (5) These properties include the costs of a shared parking structure for a complex comprised of five office buildings and one residential tower. The costs of the parking structure are allocated amongst the six buildings. (6) This property represents the 200 -unit Columbia Square - Residential tower that stabilized in 2016. (7) These costs represent infrastructure costs incurred in 1989. During the third quarter of 2009, we exercised our option to terminate the ground lease at Kilroy Airport Center, Phase IV in Long Beach, California. We had previously leased this land, which is adjacent to our Office Properties at Kilroy Airport Center, Long Beach, for potential future development opportunities. (8) These properties secure a $170.0 million mortgage note. (9) These properties secure a $91.3 million mortgage note (10) These properties are owned by Redwood City Partners LLC, a consolidated property partnership. (11) This property is owned by 303 Second Street Member LLC, a consolidated property partnership. (12) This property is owned by 100 First Street Member LLC, a consolidated property partnership. (13) These properties secure a $74.5 million mortgage note, which was repaid at par in February 2019. (14) Represents gross aggregate principal amount before the effect of the unamortized premium of approximately $0.8 million and deferred financing costs of $1.0 million as of December 31, 2018 . (15) This property is currently in the tenant improvement phase of our in-process development projects and not yet in the stabilized portfolio. The estimated rentable square feet for this property is 400,000 rentable square feet. The following table reconciles the historical cost of total real estate held for investment from January 1, 2016 to December 31, 2018 : Year Ended December 31, 2018 2017 2016 (in thousands) Total real estate held for investment, beginning of year $ 7,417,777 $ 7,060,754 $ 6,328,146 Additions during period: Acquisitions 581,671 19,829 460,957 Improvements, etc. 991,008 533,939 386,836 Total additions during period 1,572,679 553,768 847,793 Deductions during period: Cost of real estate sold (286,623 ) (191,610 ) (68,200 ) Properties held for sale — — (13,193 ) Other (277,201 ) (5,135 ) (33,792 ) Total deductions during period (563,824 ) (196,745 ) (115,185 ) Total real estate held for investment, end of year $ 8,426,632 $ 7,417,777 $ 7,060,754 The following table reconciles the accumulated depreciation from January 1, 2016 to December 31, 2018 : Year Ended December 31, 2018 2017 2016 (in thousands) Accumulated depreciation, beginning of year $ 1,264,162 $ 1,139,853 $ 994,241 Additions during period: Depreciation of real estate 198,578 190,515 171,983 Total additions during period 198,578 190,515 171,983 Deductions during period: Write-offs due to sale (71,372 ) (66,206 ) (22,471 ) Properties held for sale — — (3,900 ) Other — — — Total deductions during period (71,372 ) (66,206 ) (26,371 ) Accumulated depreciation, end of year $ 1,391,368 $ 1,264,162 $ 1,139,853

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Basis of Presentation and Significant Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements of the Company include the consolidated financial position and results of operations of the Company, the Operating Partnership, the Finance Partnership, 303 Second LLC, 100 First LLC, Redwood LLC and all of our wholly-owned and controlled subsidiaries. The consolidated financial statements of the Operating Partnership include the consolidated financial position and results of operations of the Operating Partnership, the Finance Partnership, 303 Second LLC, 100 First LLC, Redwood LLC and all of our wholly-owned and controlled subsidiaries. All intercompany balances and transactions have been eliminated in the consolidated financial statements.
Partially Owned Entities and Variable Interest Entities	Partially Owned Entities and Variable Interest Entities At December 31, 2018 the consolidated financial statements of the Company included three VIEs in addition to the Operating Partnership: 100 First LLC, 303 Second LLC and an entity established during the fourth quarter of 2018 to facilitate a Section 1031 Exchange. At December 31, 2018 , the Company and the Operating Partnership were determined to be the primary beneficiaries of these three VIEs since we had the ability to control the activities that most significantly impact each of the VIEs’ economic performance. As of December 31, 2018 , the three VIEs’ total assets, liabilities and noncontrolling interests included on our consolidated balance sheet were approximately $615.4 million (of which $543.9 million related to real estate held for investment), approximately $45.1 million and approximately $186.4 million , respectively. In January 2019, the Section 1031 Exchange was successfully completed and the related VIE was terminated. Revenues, income and net assets generated by 100 First LLC and 303 Second LLC may only be used to settle their contractual obligations, which primarily consist of operating expenses, capital expenditures and required distributions. At December 31, 2017 , the consolidated financial statements of the Company included two VIEs in addition to the Operating Partnership: 100 First LLC and 303 Second LLC. At December 31, 2017 , the impact of consolidating the VIEs increased the Company’s total assets, liabilities and noncontrolling interests on our consolidated balance sheet by approximately $426.5 million (of which $382.1 million related to real estate held for investment on our consolidated balance sheet), approximately $27.3 million and approximately $175.4 million , respectively. The consolidated financial statements of the Operating Partnership included the same three VIEs at December 31, 2017 . Our accounting policy is to consolidate entities in which we have a controlling financial interest and significant decision making control over the entity's operations. In determining whether we have a controlling financial interest in a partially owned entity and the requirement to consolidate the accounts of that entity, we consider factors such as ownership interest, board representation, management representation, size of our investment (including loans), authority to control decisions, and contractual and substantive participating rights of the members. In addition to evaluating control rights, we consolidate entities in which the other members have no substantive kick-out rights to remove the Company as the managing member. Entities in which the equity investors do not have sufficient equity at risk to finance their endeavors without additional financial support or the holders of the equity investment at risk do not have a controlling financial interest are VIEs. We evaluate whether an entity is a VIE and whether we are the primary beneficiary. We are deemed to be the primary beneficiary of a VIE when we have the power to direct the activities of the VIE that most significantly impact the VIEs’ economic performance and the obligation to absorb losses or receive benefits that could potentially be significant to the VIE. If the requirements for consolidation are not met, the Company would account for investments under the equity method of accounting if we have the ability to exercise significant influence over the entity. Equity method investments would be initially recorded at cost and subsequently adjusted for our share of net income or loss and cash contributions and distributions each period. The Company did not have any equity method investments at December 31, 2018 or 2017 .
Acquisitions	Acquisitions Subsequent to our adoption of FASB ASU No. 2017-01 (“ASU 2017-01”) on January 1, 2017, which was adopted on a prospective basis, acquisitions of operating properties and development and redevelopment opportunities generally no longer meet the definition of a business and are accounted for as asset acquisitions. For these asset acquisitions, we record the acquired tangible and intangible assets and assumed liabilities based on each asset’s and liability’s relative fair value at the acquisition date of the total purchase price plus any capitalized acquisition costs. We record the acquired tangible and intangible assets and assumed liabilities of acquisitions of operating properties and development and redevelopment opportunities that meet the accounting criteria to be accounted for as business combinations at fair value at the acquisition date. The acquired assets and assumed liabilities for an acquisition generally include but are not limited to (i) land and improvements, buildings and improvements, undeveloped land and construction in progress and (ii) identified tangible and intangible assets and liabilities associated with in-place leases, including tenant improvements, leasing costs, value of above-market and below-market operating leases and ground leases, acquired in-place lease values and tenant relationships, if any. Any debt assumed and equity (including common units of the Operating Partnership) issued in connection with a property acquisition is recorded at fair value on the date of acquisition. The fair value of land and improvements is derived from comparable sales of land and improvements within the same submarket and/or region. The fair value of buildings and improvements, tenant improvements and leasing costs considers the value of the property as if it was vacant as well as current replacement costs and other relevant market rate information. The fair value of the above-market or below-market component of an acquired in-place operating lease is based upon the present value (calculated using a market discount rate) of the difference between (i) the contractual rents to be paid pursuant to the lease over its remaining non-cancellable lease term and (ii) our estimate of the rents that would be paid using fair market rental rates and rent escalations at the date of acquisition measured over the remaining non-cancellable term of the lease for above-market operating leases and the initial non-cancellable term plus the term of any below-market fixed rate renewal options, if applicable, for below-market operating leases. Our below-market operating leases generally do not include fixed rate or below-market renewal options. The amounts recorded for above-market operating leases are included in deferred leasing costs and acquisition-related intangible assets, net on the balance sheet and are amortized on a straight-line basis as a reduction of rental income over the remaining term of the applicable leases. The amounts recorded for below-market operating leases are included in deferred revenue and acquisition-related intangible liabilities, net on the balance sheet and are amortized on a straight-line basis as an increase to rental income over the remaining term of the applicable leases plus the term of any below-market fixed rate renewal options, if applicable. The amortization of the below-market ground lease obligation is recorded as an increase to ground lease expense in the consolidated statements of operations for the periods presented. The amortization of the above-market ground lease obligation is recorded as a decrease to ground lease expense in the consolidated statements of operations for the periods presented. The fair value of acquired in-place leases is derived based on our assessment of lost revenue and costs incurred for the period required to lease the “assumed vacant” property to the occupancy level when purchased. The amount recorded for acquired in-place leases is included in deferred leasing costs and acquisition-related intangible assets, net on the balance sheet and amortized as an increase to depreciation and amortization expense over the remaining term of the applicable leases. Fully amortized intangible assets are written off each quarter. Subsequent to our adoption of ASU 2017-01 on January 1, 2017, transaction costs associated with our acquisitions are capitalized as part of the purchase price of the acquisition. Prior to our adoption of ASU 2017-01, costs associated with all operating property acquisitions and those development and redevelopment acquisitions that met the criteria to be accounted for as business combinations were expensed as incurred and costs associated with development acquisitions accounted for as asset acquisitions were capitalized as part of the cost of the asset.
Operating Properties and Cost Capitalization	Operating Properties Operating properties are generally carried at historical cost less accumulated depreciation. Properties held for sale are reported at the lower of the carrying value or the fair value less estimated cost to sell. The cost of operating properties includes the purchase price or development costs of the properties. Costs incurred for the renovation and betterment of the operating properties are capitalized to our investment in that property. Maintenance and repairs are charged to expense as incurred. When evaluating properties to be held and used for potential impairment, we first evaluate whether there are any indicators of impairment for any of our properties. If any impairment indicators are present for a specific property, we then evaluate the regional market conditions that could reasonably affect the property. If there are negative changes and trends in that regional market, we then perform an undiscounted cash flow analysis and compare the net carrying amount of the property to the property’s estimated undiscounted future cash flow over the anticipated holding period. If the estimated undiscounted future cash flow is less than the net carrying amount of the property, we then perform an impairment loss calculation to determine if the fair value of the property is less than the net carrying value of the property. Our impairment loss calculation compares the net carrying amount of the property to the property’s estimated fair value, which may be based on estimated discounted future cash flow calculations or third-party valuations or appraisals. We would recognize an impairment loss if the asset’s net carrying amount exceeds the asset’s estimated fair value. If we were to recognize an impairment loss, the estimated fair value of the asset (less costs to sell for assets held for sale) would become its new cost basis. For a depreciable long-lived asset, the new cost basis would be depreciated (amortized) over the remaining useful life of that asset. Cost Capitalization All costs clearly associated with the development, redevelopment and construction of a property are capitalized as project costs, including internal compensation costs. In addition, the following costs are capitalized as project costs during periods in which activities necessary to prepare development and redevelopment properties for their intended use are in progress: pre-construction costs essential to the development of the property, interest, real estate taxes and insurance. • For office and retail development and redevelopment properties that are pre-leased, we cease capitalization when revenue recognition commences, which is upon substantial completion of tenant improvements deemed to be the Company’s asset for accounting purposes. • For office and retail development and redevelopment properties that are not pre-leased, we may not immediately build out the tenant improvements. Therefore, we cease capitalization when revenue recognition commences upon substantial completion of the tenant improvements deemed to be the Company's asset for accounting purposes, but in any event, no later than one year after the cessation of major construction activities. We also cease capitalization on a development or redevelopment property when activities necessary to prepare the property for its intended use have been suspended. • For office and retail development or redevelopment properties with multiple tenants and staged leasing, we cease capitalization and begin depreciation on the portion of the development or redevelopment property for which revenue recognition has commenced. • For residential development properties, we cease capitalization when the property is substantially complete and available for occupancy. Once major base building construction activities have ceased and the development or redevelopment property is placed in service, the costs capitalized to construction in progress are transferred to land and improvements, buildings and improvements, and deferred leasing costs on our consolidated balance sheets as the historical cost of the property. Depreciation and Amortization of Buildings and Improvements The costs of buildings and improvements and tenant improvements are depreciated using the straight-line method of accounting over the estimated useful lives set forth in the table below.
Real Estate Assets Held for Sale, Dispositions and Discontinued Operations	Real Estate Assets Held for Sale, Dispositions and Discontinued Operations A real estate asset is classified as held for sale when certain criteria are met, including but not limited to the availability of the asset for immediate sale, the existence of an active program to locate a buyer and the probable sale or transfer of the asset within one year. If such criteria are met, we present the applicable assets and liabilities related to the real estate asset held for sale, if material, separately on the balance sheet and we would cease to record depreciation and amortization expense. Real estate assets held for sale are reported at the lower of their carrying value or their estimated fair value less the estimated costs to sell. As of December 31, 2018 and 2017 , we did not have any properties classified as held for sale. Property disposals representing a strategic shift that have (or will have) a major effect on the Company’s operations and financial results, such as a major line of business, a major geographical area or a major equity investment, are required to be presented as discontinued operations. If we were to determine that a property disposition represents a strategic shift, the revenues, expenses and net gain (loss) on dispositions of the property would be recorded in discontinued operations for all periods presented through the date of the applicable disposition. The operations of the eleven , eleven and six properties sold during the years ended December 31, 2018 , December 31, 2017 and December 31, 2016 , respectively, are presented in continuing operations as they did not represent a strategic shift in the Company’s operations and financial results. The net gains (losses) on dispositions of non-depreciable real estate property, including land, are reported in the consolidated statements of operations as gains (losses) on sale of land within continuing operations in the period the land is sold. The net gains (losses) on dispositions of depreciable real estate property are reported in the consolidated statements of operations as gains on sales of depreciable operating properties within continuing operations in the period the land is sold
Revenue Recognition, Tenant Reimbursements and Other Property Income	Revenue Recognition We recognize revenue from rent, tenant reimbursements, parking and other revenue once all of the following criteria are met: (i) the agreement has been fully executed and delivered, (ii) services have been rendered, (iii) the amount is fixed or determinable and (iv) the collectability of the amount is reasonably assured. Minimum annual rental revenues are recognized in rental revenues on a straight-line basis over the non-cancellable term of the related lease. Rental revenue recognition commences when the tenant takes possession or controls the physical use of the leased space. In order for the tenant to take possession, the leased space must be substantially complete and ready for its intended use. In order to determine whether the leased space is substantially ready for its intended use, we begin by determining whether the Company or the tenant owns the tenant improvements. When we conclude that the Company is the owner of tenant improvements, rental revenue recognition begins when the tenant takes possession of the finished space, which is generally when Company owned tenant improvements are substantially complete. In certain instances, when we conclude that the Company is not the owner (the tenant is the owner) of tenant improvements, rental revenue recognition begins when the tenant takes possession of or controls the space. When we conclude that the Company is the owner of tenant improvements, we record the cost to construct the tenant improvements, including costs paid for or reimbursed by the tenants, as a capital asset. For these tenant improvements, we record the amount funded by or reimbursed by the tenants as deferred revenue, which is amortized on a straight-line basis as additional rental income over the term of the related lease. When we conclude that the tenant is the owner of tenant improvements for accounting purposes, we record our contribution towards those improvements as a lease incentive, which is included in deferred leasing costs and acquisition-related intangible assets, net on our consolidated balance sheets and amortized as a reduction to rental income on a straight-line basis over the term of the lease. For residential properties, we commence revenue recognition upon lease commencement. Residential rental revenue is recognized on a straight-line basis over the term of the related lease, net of any concessions. Tenant Reimbursements Reimbursements from tenants, consisting of amounts due from tenants for common area maintenance, real estate taxes and other recoverable costs, are recognized as revenue in the period the recoverable costs are incurred. Tenant reimbursements are generally recognized and recorded on a gross basis, as we are generally the primary obligor with respect to purchasing goods and services from third-party suppliers, have discretion in selecting the supplier, and have credit risk. Other Property Income Other property income primarily includes amounts recorded in connection with lease terminations, tenant bankruptcy settlement payments, broken deal income and property damage settlement related payments. Lease termination fees are amortized over the remaining lease term, if applicable. If there is no remaining lease term, they are recognized when received and realized. Other property income also includes miscellaneous income from tenants, such as fees related to the restoration of leased premises to their original condition and fees for late rental payments.
Allowances for Uncollectible Tenant and Deferred Rent Receivables	Allowances for Uncollectible Tenant and Deferred Rent Receivables We carry our current and deferred rent receivables net of allowances for uncollectible amounts. Our determination of the adequacy of these allowances is based primarily upon evaluations of individual receivables, current economic conditions, and other relevant factors. The allowances are increased or decreased through the provision for bad debts on our consolidated statements of operations.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly-liquid investments with original maturities of three months or less to be cash equivalents
Restricted Cash	Restricted Cash Restricted cash consists of cash proceeds from dispositions that are temporarily held at qualified intermediaries for purposes of facilitating potential Section 1031 Exchanges and cash held in escrow related to acquisition and disposition holdbacks. Restricted cash also includes cash held as collateral to provide credit enhancement for the Operating Partnership’s mortgage debt, including cash reserves for capital expenditures, tenant improvements and property taxes. As of December 31, 2018 we had $113.1 million of restricted cash held at qualified intermediaries for the purpose of facilitating Section 1031 Exchanges. In January 2019, the Section 1031 Exchange was completed and the cash proceeds were released from the qualified intermediary. We did not have any restricted cash held at qualified intermediaries for the purpose of facilitating Section 1031 Exchanges at December 31, 2017 .
Marketable Securities	Marketable securities reported in our consolidated balance sheets represent the assets held in connection with the Kilroy Realty Corporation 2007 Deferred Compensation Plan (the “Deferred Compensation Plan”) (see Note 16 “Employee Benefit Plans” for additional information). The Deferred Compensation Plan assets are held in a limited rabbi trust and invested in various mutual and money market funds. As a result, the marketable securities are treated as trading securities for financial reporting purposes and are adjusted to fair value at the end of each accounting period, with the corresponding gains and losses recorded in interest income and other net investment gains (losses).
Deferred Compensation Plan	At the time eligible management employees (“Participants”) defer compensation or earn mandatory Company contributions, or if we were to make a discretionary contribution, we record compensation cost and a corresponding deferred compensation plan liability, which is included in accounts payable, accrued expenses, and other liabilities on our consolidated balance sheets. This liability is adjusted to fair value at the end of each accounting period based on the performance of the benchmark funds selected by each Participant, and the impact of adjusting the liability to fair value is recorded as an increase or decrease to compensation cost. The impact of adjusting the deferred compensation plan liability to fair value and the changes in the value of the marketable securities held in connection with the Deferred Compensation Plan generally offset and therefore do not significantly impact net income.
Deferred Leasing Costs	Deferred Leasing Costs Costs incurred in connection with successful property leasing are capitalized as deferred leasing costs and classified as investing activities in the statement of cash flows. Deferred leasing costs consist primarily of leasing commissions and also include certain internal payroll costs and lease incentives, which are amortized using the straight-line method of accounting over the lives of the leases which generally range from one to 20 years. We reevaluate the remaining useful lives of leasing costs as the creditworthiness of our tenants and economic and market conditions change. If we determine that the estimated remaining life of a lease has changed, we adjust the amortization period accordingly. Fully amortized deferred leasing costs are written off each quarter. As discussed below under “ Accounting Standards Issued But Not Yet Effective at December 31, 2018 ,” upon the adoption of FASB ASU No. 2016-02 “Leases (Topic 842),” most deferred leasing costs (with the exception of leasing commissions paid to external third party brokers) will no longer meet the criteria for capitalization. For leases commenced prior to December 31, 2018, these costs will continue to be amortized over the remaining life of the associated lease. For leases executed prior to December 31, 2018 that have not yet commenced as of December 31, 2018, such costs will be charged to distributions in excess of earnings as of January 1, 2019.
Deferred Financing Costs, and Debt Discounts and Premiums	Deferred Financing Costs Financing costs related to the origination or assumption of long-term debt are deferred and generally amortized using the straight-line method of accounting, which approximates the effective interest method, over the contractual terms of the applicable financings. Fully amortized deferred financing costs are written off when the corresponding financing is repaid. Debt Discounts and Premiums Original issuance debt discounts and discounts/premiums related to recording debt acquired in connection with operating property acquisitions at fair value are generally amortized and accreted on a straight-line basis, which approximates the effective interest method. Discounts are recorded as additional interest expense from date of issuance or acquisition through the contractual maturity date of the related debt. Premiums are recorded as a reduction to interest expense from the date of issuance or acquisition through the contractual maturity date of the related debt.
Noncontrolling Interest and Partnership Interests	Noncontrolling Interests - Common Units of the Operating Partnership in the Company's Consolidated Financial Statements Common units of the Operating Partnership within noncontrolling interests in the Company’s consolidated financial statements represent the common limited partnership interests in the Operating Partnership not held by the Company (“noncontrolling common units”). Noncontrolling common units are presented in the equity section of the Company’s consolidated balance sheets and are reported at their proportionate share of the net assets of the Operating Partnership. Noncontrolling interests with redemption provisions that permit the issuer to settle in either cash or shares of common stock must be further evaluated to determine whether equity or temporary equity classification on the balance sheet is appropriate. Since the common units contain such a provision, we evaluated the accounting guidance and determined that the common units qualify for equity presentation in the Company’s consolidated financial statements. Net income attributable to noncontrolling common units is allocated based on their relative ownership percentage of the Operating Partnership during the reported period. The noncontrolling interest ownership percentage is determined by dividing the number of noncontrolling common units by the total number of common units outstanding. The issuance or redemption of additional shares of common stock or common units results in changes to the noncontrolling interest percentage as well as the total net assets of the Company. As a result, all equity transactions result in an allocation between equity and the noncontrolling interest in the Company’s consolidated balance sheets and statements of equity to account for the changes in the noncontrolling interest ownership percentage as well as the change in total net assets of the Company. Noncontrolling Interests in Consolidated Property Partnerships Noncontrolling interests in consolidated property partnerships represent the equity interests held by unrelated third parties in our three consolidated property partnerships (see Note 11 “Noncontrolling Interests on the Company’s Consolidated Financial Statements” and see Note 12 “Noncontrolling Interests on the Operating Partnership’s Consolidated Financial Statements”). Noncontrolling interests in consolidated property partnerships are not redeemable and are presented as permanent equity in the Company's consolidated balance sheets. We account for the noncontrolling interests in consolidated property partnerships using the hypothetical liquidation at book value (“HLBV”) method to attribute the earnings or losses of the consolidated property partnerships between the controlling and noncontrolling interests. Under the HLBV method, the amounts reported as noncontrolling interests in consolidated property partnerships in the consolidated balance sheets represent the amounts the noncontrolling interests would hypothetically receive at each balance sheet reporting date under the liquidation provisions of the governing agreements assuming the net assets of the consolidated property partnerships were liquidated at recorded amounts and distributed between the controlling and noncontrolling interests in accordance with the governing documents. The net income attributable to noncontrolling interests in consolidated property partnerships in the consolidated statements of operations is associated with the increase or decrease in the noncontrolling interest holders’ contractual claims on the respective entities’ balance sheets assuming a hypothetical liquidation at the end of that reporting period when compared with their claims on the respective entities’ balance sheets assuming a hypothetical liquidation at the beginning of that reporting period, after removing any contributions or distributions. Common Partnership Interests on the Operating Partnership’s Consolidated Balance Sheets The common units held by the Company and the noncontrolling common units held by the common limited partners are both presented in the permanent equity section of the Operating Partnership’s consolidated balance sheets in partners’ capital. The redemption rights of the noncontrolling common units permit us to settle the redemption obligation in either cash or shares of the Company’s common stock at our option (see Note 11 “Noncontrolling Interests on the Company’s Consolidated Financial Statements” for additional information). Noncontrolling Interests on the Operating Partnership’s Consolidated Financial Statements Noncontrolling interests in the Operating Partnership’s consolidated financial statements include the noncontrolling interest in property partnerships (see Note 12 “Noncontrolling Interests on the Operating Partnership’s Consolidated Financial Statements”) and the Company’s 1.0% general partnership interest in the Finance Partnership. The 1.0% general partnership interest in the Finance Partnership noncontrolling interest is presented in the permanent equity section of the Operating Partnership’s consolidated balance sheets given that these interests are not convertible or redeemable into any other ownership interest of the Company or the Operating Partnership.
Equity Offerings	Equity Offerings Underwriting commissions and offering costs incurred in connection with common equity offerings and our at-the-market stock offering program (see Note 13 “Stockholders’ Equity of the Company”) are reflected as a reduction of additional paid-in capital. Issuance costs incurred in connection with preferred equity offerings are reflected as a reduction of the carrying value of the preferred equity. Sales of our common stock under forward equity sale agreements (such as those under the forward equity offering executed in August 2018 and discussed at Note 13) meet the derivatives and hedging guidance scope exception to be accounted for as equity instruments based on the following assessment: (i) none of the agreements’ exercise contingencies were based on observable markets or indices besides those related to the market for our own stock price and operations; and (ii) none of the settlement provisions precluded the agreements from being indexed to our own stock. The net proceeds from any equity offering of the Company are generally contributed to the Operating Partnership in exchange for a number of common units equivalent to the number of shares of common stock issued and are reflected in the Operating Partnership’s consolidated financial statements as an increase in partners’ capital.
Share-based Incentive Compensation Accounting	Share-based Incentive Compensation Accounting Compensation cost for all share-based awards, including options, requires measurement at estimated fair value on the grant date. Compensation cost is recognized on a straight-line basis over the service vesting period, which represents the requisite service period. The grant date fair value of market measure-based share-based compensation plans are calculated using a Monte Carlo simulation pricing model. The grant date fair value of stock option grants is calculated using the Black-Scholes valuation model. Equity awards settled in cash are valued at the fair value of our common stock on the period end date through the settlement date. Equity awards settled in cash are remeasured at each reporting period and are recognized as a liability in the consolidated balance sheet during the vesting period until settlement. Forfeitures of all share-based awards are recognized when they occur. For share-based awards in which the performance period precedes the grant date, we recognize compensation cost over the requisite service period, which includes both the performance and service vesting periods, using the accelerated attribution expense method. The requisite service period begins on the date the Executive Compensation Committee authorizes the award and adopts any relevant performance measures. For share-based awards with performance-based measures, the total estimated compensation cost is based on our most recent estimate of the probable achievement of the pre-established specific corporate performance measures. These estimates are based on actual results and our latest internal forecasts for each performance measure. For share-based awards with market measures, the total estimated compensation cost is based on the fair value of the award at the grant date. For share-based awards with performance-based measures and market measures, the total estimated compensation cost is based on the fair value per share at the grant date multiplied by our most recent estimate of the number of shares to be earned based on actual results and the probable achievement of the pre-established corporate performance measures based on our latest internal forecasts. In accordance with the provisions of our share-based incentive compensation plan, we accept the return of shares of Company common stock, at the current quoted market price, from employees to satisfy minimum statutory tax-withholding requirements related to shares that vested during the period. For share-based awards granted by the Company, the Operating Partnership issues a number of common units equal to the number of shares of common stock ultimately granted by the Company in respect of such awards.
Basic and Diluted Net Income Available to Common Stockholders/ Unitholders per Share/ Unit	Basic and Diluted Net Income Available to Common Stockholders per Share Basic net income available to common stockholders per share is computed by dividing net income available to common stockholders, after preferred distributions and the allocation of income to participating securities, by the weighted-average number of shares of common stock outstanding for the period. Diluted net income available to common stockholders per share is computed by dividing net income available for common stockholders, after preferred distributions and the allocation of income to participating securities, by the sum of the weighted-average number of shares of common stock outstanding for the period plus the assumed exercise of all dilutive securities. The impact of the outstanding common units is considered in the calculation of diluted net income available to common stockholders per share. The common units are not reflected in the diluted net income available to common stockholders per share calculation because the exchange of common units into common stock is on a one for one basis, and the common units are allocated net income on a per share basis equal to the common stock (see Note 21 “Net Income Available to Common Stockholders Per Share of the Company”). Accordingly, any exchange would not have any effect on diluted net income (loss) available to common stockholders per share. Nonvested share-based payment awards (including nonvested restricted stock units (“RSUs”), vested market-measure RSUs and vested dividend equivalents issued to holders of RSUs) containing nonforfeitable rights to dividends or dividend equivalents are accounted for as participating securities and included in the computation of basic and diluted net income available to common stockholders per share pursuant to the two-class method. The dilutive effect of shares issuable under executed forward equity sale agreements and stock options are reflected in the weighted average diluted outstanding shares calculation by application of the treasury stock method. The dilutive effect of the outstanding nonvested shares of common stock (“nonvested shares”) and RSUs that have not yet been granted but are contingently issuable under the share-based compensation programs is reflected in the weighted average diluted shares calculation by application of the treasury stock method at the beginning of the quarterly period in which all necessary conditions have been satisfied. Basic and Diluted Net Income Available to Common Unitholders per Unit Basic net income available to common unitholders per unit is computed by dividing net income available to common unitholders, after preferred distributions and the allocation of income to participating securities, by the weighted-average number of vested common units outstanding for the period. Diluted net income available to common unitholders per unit is computed by dividing net income available to common unitholders, after preferred distributions and the allocation of income to participating securities, by the sum of the weighted-average number of common units outstanding for the period plus the assumed exercise of all dilutive securities. The dilutive effect of stock options, outstanding nonvested shares, RSUs, awards containing nonforfeitable rights to dividend equivalents and shares issuable under executed forward equity sale agreements are reflected in diluted net income available to common unitholders per unit in the same manner as noted above for net income available to common stockholders per share.
Fair Value Measurements	Fair Value Measurements The fair values of our financial assets and liabilities are disclosed in Note 19, “Fair Value Measurements and Disclosures,” to our consolidated financial statements. The only financial assets recorded at fair value on a recurring basis in our consolidated financial statements are our marketable securities. We elected not to apply the fair value option for any of our eligible financial instruments or other items. We determine the estimated fair value of financial assets and liabilities utilizing a hierarchy of valuation techniques based on whether the inputs to a fair value measurement are considered to be observable or unobservable in a marketplace. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect our market assumptions. This hierarchy requires the use of observable market data when available. The following is the fair value hierarchy: • Level 1 – quoted prices for identical instruments in active markets; • Level 2 – quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active and model-derived valuations in which significant inputs and significant value drivers are observable in active markets; and • Level 3 – fair value measurements derived from valuation techniques in which one or more significant inputs or significant value drivers are unobservable. We determine the fair value for the marketable securities using quoted prices in active markets for identical assets. Our other financial instruments, which are only disclosed at fair value, are comprised of secured debt, unsecured senior notes, unsecured line of credit and unsecured term loan facility. We generally determine the fair value of our secured debt, unsecured debt, and unsecured line of credit by performing discounted cash flow analyses using an appropriate market discount rate. We calculate the market rate by obtaining period-end treasury rates for maturities that correspond to the maturities of our fixed-rate debt and then adding an appropriate credit spread based on information obtained from third-party financial institutions. These credit spreads take into account factors, including but not limited to, our credit profile, the tenure of the debt, amortization period, whether the debt is secured or unsecured, and the loan-to-value ratio of the debt to the collateral. These calculations are significantly affected by the assumptions used, including the discount rate, credit spreads and estimates of future cash flow. We calculate the market rate of our unsecured line of credit, unsecured term loan facility, and unsecured term loan by obtaining the period-end London Interbank Offered Rate (“LIBOR”) and then adding an appropriate credit spread based on our credit ratings, and the amended terms of our unsecured line of credit, unsecured term loan facility, and unsecured term loan agreement. We determine the fair value of each of our publicly traded unsecured senior notes based on their quoted trading price at the end of the reporting period, if such prices are available. Carrying amounts of our cash and cash equivalents, restricted cash and accounts payable approximate fair value due to their short-term maturities.
Income Taxes	Income Taxes We have elected to be taxed as a REIT under Sections 856 through 860 of the Code. To qualify as a REIT, we must distribute annually at least 90% of our adjusted taxable income, as defined in the Code, to our stockholders and satisfy certain other organizational and operating requirements. We generally will not be subject to federal income taxes if we distribute 100% of our taxable income for each year to our stockholders. If we fail to qualify as a REIT in any taxable year, we will be subject to federal income taxes (including any applicable alternative minimum tax) on our taxable income at regular corporate rates and we may not be able to qualify as a REIT for four subsequent taxable years. Even if we qualify for taxation as a REIT, we may be subject to certain state and local taxes on our income and property and to federal income taxes and excise taxes on our undistributed taxable income. We believe that we have met all of the REIT distribution and technical requirements for the years ended December 31, 2018 , 2017 and 2016 , and we were not subject to any federal income taxes (see Note 25 “Tax Treatment of Distributions” for additional information). We intend to continue to adhere to these requirements and maintain the Company’s REIT status. Accordingly, no provision for income taxes has been made in the accompanying financial statements. In addition, any taxable income from our taxable REIT subsidiaries, which were formed in 2002 and 2018, are subject to federal, state, and local income taxes. For the years ended December 31, 2018 , 2017 and 2016 the taxable REIT subsidiaries had de minimis taxable income.
Uncertain Tax Positions	Uncertain Tax Positions We include favorable tax positions in the calculation of tax liabilities if it is more likely than not that our adopted tax position will prevail if challenged by tax authorities. We evaluated the potential impact of identified uncertain tax positions for all tax years still subject to audit under state and federal income tax law and concluded that we did not have any unrecognized tax benefits or any additional tax liabilities as of December 31, 2018 or 2017 . As of December 31, 2018 , the years still subject to audit are 2014 through 2018 under the California state income tax law and 2015 through 2018 under the federal income tax law.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates.
Segment	Segments We currently operate in one operating segment, our office properties segment.
Concentration of Credit Risk	Concentration of Credit Risk All of our properties and development and redevelopment projects are owned and all of our business is currently conducted in the state of California with the exception of the ownership and operation of eight office properties and one development project under construction located in the state of Washington. The ability of tenants to honor the terms of their leases is dependent upon the economic, regulatory, and social factors affecting the communities in which our tenants operate. As of December 31, 2018 , our 15 largest tenants represented approximately 45.7% of total annualized base rental revenues, of which 5.9% was attributable to our largest tenant. We have deposited cash with financial institutions that is insured by the Federal Deposit Insurance Corporation (“FDIC”) up to $250,000 per institution. As of December 31, 2018 and 2017 , we had cash accounts in excess of FDIC insured limits.
Recent Accounting Pronouncements	Accounting Pronouncements Adopted January 1, 2019 ASU No. 2016-02 “Leases (Topic 842)” On February 25, 2016, the FASB issued ASU No. 2016-02 “Leases (Topic 842)” (“ASU 2016-02”) to amend the accounting guidance for leases. The accounting applied by a lessor is largely unchanged under ASU 2016-02. However, the standard requires lessees to recognize lease assets and lease liabilities for leases classified as operating leases on the balance sheet. Lessees will recognize in the statement of financial position a liability to make lease payments and a right-of-use asset representing its right to use the underlying asset for the lease term. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize lease assets and lease liabilities. If a lessee makes this election, it will recognize lease expense for such leases generally on a straight-line basis over the lease term. For leases with a term of 12 months or less where we are the lessee, we plan to make this policy election. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018. In July 2018, the FASB issued ASU No. 2018-11 which (1) simplifies transition requirements for both lessees and lessors by adding an option that permits an organization to apply the transition provisions of the new standard at its adoption date instead of at the earliest comparative period presented in its financial statements and (2) provides a practical expedient for lessors that permits lessors to make an accounting policy election to not separate nonlease components from the associated lease components, if the following two criteria are met: (1) the timing and pattern of transfer of the lease and nonlease components are the same and (2) the lease component would be classified as an operating lease if accounted for separately. For leases where we are the lessor, we plan to elect the optional transition relief and apply the practical expedients provided by ASU 2018-11. As a result, leases where we are the lessor will be accounted for in a similar method to existing standards with the underlying leased asset being reported and recognized as a real estate asset. In December 2018, the FASB issued ASU 2018-20 which clarifies lessor treatment of sales taxes and other similar taxes collected from lessees, lessor costs paid directly by lessees and recognition of variable payments for contracts with lease and nonlease components. This will result in a gross-up of amounts recorded to tenant reimbursements and property expenses in our consolidated statements of operations related to certain services that, under existing GAAP guidance, were presented on a net basis and such change will not have an impact to net income. ASU 2016-02 also specifies that upon adoption, lessors will no longer be able to capitalize and amortize certain leasing related costs and instead will only be permitted to capitalize and amortize incremental direct leasing costs. As a result, we have concluded that upon the adoption of the standard, we will be required to expense as incurred certain leasing costs we are currently able to capitalize and amortize as deferred leasing costs under existing guidance. This change had a material impact on the Company’s consolidated financial statements upon adoption of the standard on January 1, 2019. The election of the package of practical expedients described above permits us to continue to account for our leases that commenced before January 1, 2019 under the existing lease accounting guidance for the remainder of their lease terms, and to apply the new lease accounting guidance to leases commencing or modified after January 1, 2019. On January 1, 2019, we recognized a cumulative adjustment to distributions in excess of earnings, as required by ASU 2016-02, to write-off lease origination costs that were capitalized in connection with leases that had not commenced before January 1, 2019. These costs were capitalized in accordance with the lease accounting standards existing prior to January 1, 2019, and would not qualify for capitalization under the new lease accounting guidance. This adjustment did not have a material impact to our consolidated financial statements. For leases where we are the lessee, specifically for our four ground leases, the adoption of the standard will significantly change the accounting on our consolidated balance sheets since both existing ground leases and any future ground leases will be required to be recorded on the Company’s consolidated balance sheets as an obligation of the Company. Existing ground leases executed before the January 1, 2019 adoption date will continue to be accounted for as operating leases and the new guidance will not have a material impact on our recognition of ground lease expense or our results of operations. However, we will be required to recognize a right of use asset and a lease liability on our consolidated balance sheets equal to the present value of the minimum lease payments required in accordance with each ground lease. The adoption of this ASU will result in the recognition of operating lease right of use assets and related liabilities of approximately $80 million to $95 million in the aggregate as of January 1, 2019. We do not expect there will be a material impact to our consolidated statements of operations or consolidated cash flows as a result of adoption of this new guidance. In addition, we currently believe that for new ground leases entered into after the adoption date of the new standard, such leases could be required to be accounted for as financing-type leases, resulting in ground lease expense recorded using the effective interest method instead of on a straight-line basis over the term of the lease. This could have a significant impact on our results of operations if we enter into material new ground leases after the date of adoption since ground lease expense calculated using the effective interest method results in an increased amount of ground lease expense in the earlier years of a ground lease as compared to the current straight-line method. Accounting Pronouncements Effective 2020 and Beyond ASU No. 2016-13 “Financial Instruments - Credit Losses (Topic 326)” On June 16, 2016, the FASB issued ASU No. 2016-13 (“ASU 2016-13”) to amend the accounting for credit losses for certain financial instruments. Under the new guidance, an entity recognizes its estimate of expected credit losses as an allowance, which the FASB believes will result in more timely recognition of such losses. In November 2018, the FASB released ASU No. 2018-19 “ Codification Improvements to Topic 326, Financial Instruments - Credit Losses. ” This ASU clarifies that receivables arising from operating leases are not within the scope of Subtopic 326-20 “Financial Instruments – Credit Losses.” Instead, impairment of receivables arising from operating leases should be accounted for under Subtopic 842-30 “Leases – Lessor.” ASU 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. The Company does not anticipate that the guidance will have an impact on the consolidated financial statements or notes to the consolidated financial statements. ASU No. 2018-13 “Fair Value Measurement (Topic 820)” On August 28, 2018, the FASB issued ASU No. 2018-13 (“ASU 2018-13”) to amend the disclosure requirements for fair value measurements. The amendments in ASU 2018-13 include new, modified and eliminated disclosure requirements and are the result of a broader disclosure project called FASB Concepts Statement, Conceptual Framework for Financial Reporting - Chapter 8: Notes to Financial Statements , which the Board finalized on August 28, 2018. The Board used the guidance in the Concepts Statement to improve the effectiveness of ASC 820’s disclosure requirements. ASU 2018-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for any eliminated or modified disclosures. The Company currently anticipates that the guidance will not have a significant impact on the disclosures in the notes to the consolidated financial statements. ASU No. 2018-15 “Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40)” On August 29, 2018, the FASB issued ASU No. 2018-15 (“ASU 2018-15”) to amend a customer’s accounting for implementation costs incurred in a cloud computing arrangement that is a service contract. ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). ASU 2018-15 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted, including adoption in any interim period. ASU 2018-15 can be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company is currently evaluating the impact of ASU 2018-15 on the consolidated financial statements and notes to the consolidated financial statements.

Organization and Ownership (Tab

Organization and Ownership (Tables)	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of real estate properties	Our stabilized portfolio of operating properties was comprised of the following properties at December 31, 2018 : Number of Buildings Rentable Square Feet (unaudited) Number of Tenants Percentage Occupied (unaudited) Percentage Leased (unaudited) Stabilized Office Properties 94 13,232,580 482 94.4 % 96.6 % Number of Number of Units 2018 Average Occupancy Stabilized Residential Property 1 200 79.7 % As of December 31, 2018 , the following properties were excluded from our stabilized portfolio. We did not have any redevelopment properties or properties held for sale at December 31, 2018 . Number of Properties/Projects Estimated Rentable Square Feet (1) (unaudited) In-process development projects - tenant improvement (2) 2 1,150,000 In-process development projects - under construction (3) 3 1,290,000 _______________ (1) Estimated rentable square feet upon completion. (2) Includes 88,000 square feet of Production, Distribution, and Repair (“PDR”) space. (3) In addition to the estimated office and PDR rentable square feet noted above, development projects under construction also include 96,000 square feet of retail space and 801 residential units.

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Basis of Presentation and Significant Accounting Policies [Abstract]
Buildings, improvements, and tenant improvements depreciation	Asset Description Depreciable Lives Buildings and improvements 25 – 40 years Tenant improvements 1 – 20 years (1) ________________________ (1) Tenant improvements are amortized over the shorter of the lease term or the estimated useful life.

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2018
Asset Acquisitions [Abstract]
Schedule of Acquisitions	The acquisition was funded with proceeds from the Company’s unsecured revolving credit facility and the Company’s at-the-market stock offering program. Project Date of Acquisition City/Submarket Type Purchase Price (in millions) (1) Kilroy Oyster Point June 1, 2018 South San Francisco Land $ 308.2 ________________________ (1) Excludes acquisition-related costs. In connection with this acquisition, we also recorded $40.6 million in accrued liabilities and environmental remediation liabilities at the date of acquisition, which are not included in the purchase price above. As of December 31, 2018 , the purchase price and our current estimate of assumed liabilities are included in undeveloped land and construction in progress and the assumed liabilities are included in accounts payable, accrued expenses and other liabilities on the Company’s consolidated balance sheets. During the year ended December 31, 2018, we acquired the four operating properties listed below in two transactions from unrelated third parties. We did not acquire any operating properties during the year ended December 31, 2017 . Property Date of Acquisition Number of Buildings Rentable Square Feet (unaudited) Occupancy as of December 31, 2018 (unaudited) Purchase Price (in millions) (1) 2018 Acquisitions 345, 347 & 349 Oyster Point Boulevard, South San Francisco, CA January 31, 2018 3 145,530 78.5 % $ 111.0 345 Brannan Street, San Francisco, CA (2) December 21, 2018 1 110,030 99.7 % 146.0 Total (3) 4 255,560 $ 257.0 ________________________ (1) Excludes acquisition-related costs. (2) At December 31, 2018 , this property was temporarily being held in a separate VIE to facilitate potential Section 1031 Exchanges. During January 2019, the Company completed the Section 1031 Exchange related to this VIE. See Note 2 “Basis of Presentation and Significant Accounting Policies.” (3) The results of operations for the properties acquired during 2018 contributed $8.0 million and $1.7 million to revenue and net income, respectively, for the year ended December 31, 2018.
Schedule of estimated fair values of the assets acquired and liabilities assumed	The related assets, liabilities and results of operations of the acquired properties are included in the consolidated financial statements as of the date of acquisition. The following table summarizes the estimated fair values of the assets and liabilities assumed at the respective acquisition dates for our 2018 operating property acquisitions: Total 2018 Operating Property Acquisitions (1) Assets Land and improvements $ 80,269 Buildings and improvements (2) 172,059 Deferred leasing costs and acquisition-related intangible assets (3) 13,593 Total assets acquired $ 265,921 Liabilities Acquisition-related intangible liabilities (4) $ 8,921 Total liabilities assumed 8,921 Net assets and liabilities acquired $ 257,000 ________________________ (1) The purchase price of the two acquisitions completed during the year ended December 31, 2018 were individually less than 5% and in aggregate less than 10% of the Company’s total assets as of December 31, 2017 . (2) Represents buildings, building improvements and tenant improvements. (3) Represents in-place leases (approximately $11.8 million with a weighted average amortization period of 1.3 years years) and leasing commissions (approximately $1.8 million with a weighted average amortization period of 6.6 years years). (4) Represents below-market leases (approximately $8.9 million with a weighted average amortization period of 9.8 years years).

Dispositions (Tables)

Dispositions (Tables)	12 Months Ended
	Dec. 31, 2018
Discontinued Operations and Disposal Groups [Abstract]
Schedule operating properties and land dispositions	The following table summarizes the operating properties sold during the years ended December 31, 2018 , 2017 and 2016 : Location Month of Disposition Number of Buildings Rentable Square Feet (unaudited) Sales Price (in millions) (1) 2018 Dispositions 1310-1327 Chesapeake Terrace, Sunnyvale, CA November 4 266,982 $ 160.3 Plaza Yarrow Bay Properties (2) November 4 279,924 134.5 23925, 23975, & 24025 Park Sorrento, Calabasas, CA December 3 225,340 78.2 Total 2018 Dispositions 11 772,246 $ 373.0 2017 Dispositions 5717 Pacific Center Boulevard, San Diego, CA January 1 67,995 $ 12.1 Sorrento Mesa and Mission Valley Properties (3) September 10 675,143 174.5 Total 2017 Dispositions 11 743,138 $ 186.6 2016 Dispositions Torrey Santa Fe Properties (4) January 4 465,812 $ 262.3 4930, 4939 & 4955 Directors Place, San Diego, CA (5) July 2 136,908 49.0 Total 2016 Dispositions 6 602,720 $ 311.3 __________________ (1) Represents gross sales price before the impact of broker commissions and closing costs. (2) The Plaza Yarrow Bay Properties include the following properties: 10210, 10220 and 10230 NE Points Drive & 3933 Lake Washington Boulevard NE in Kirkland, Washington. (3) The Sorrento Mesa and Mission Valley Properties includes the following properties: 10390, 10394, 10398, 10421, 10445 and 10455 Pacific Center Court, 2355, 2365, 2375 and 2385 Northside Drive and Pacific Corporate Center - Lot 8, a 5.0 acre undeveloped land parcel. (4) The Torrey Santa Fe Properties include the following properties: 7525, 7535, 7545 and 7555 Torrey Santa Fe. (5) Includes two operating properties totaling 136,908 rentable square feet and a 7.0 acre undeveloped land parcel. The following table summarizes the land dispositions completed during the year ended December 31, 2016 : Properties Submarket Month of Disposition Gross Site Acreage (unaudited) Sales Price (1) (in millions) 2016 Land Dispositions Carlsbad Oaks - Lot 7 Carlsbad January 7.6 $ 4.5 Carlsbad Oaks - Lots 4 & 5 Carlsbad June 11.2 6.0 Carlsbad Oaks - Lot 8 Carlsbad June 13.2 8.9 Total 2016 Land Dispositions (2)(3) 32.0 $ 19.4 __________________ (1) Represents gross sales price before the impact of commissions and closing costs. (2) In connection with these land dispositions, $2.3 million of secured debt was assumed by the buyers. (3) The 2016 land dispositions resulted in a net loss on sales of $0.3 million .

Deferred Leasing Costs and Ac_2

Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, net (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of identified deferred leasing costs and acquisition-related intangible assets	The following table summarizes our deferred leasing costs and acquisition-related intangible assets (acquired value of leasing costs, above-market operating leases, in-place leases and below-market ground lease obligation) and intangible liabilities (acquired value of below-market operating leases and above-market ground lease obligation) as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Deferred Leasing Costs and Acquisition-related Intangible Assets, net: Deferred leasing costs $ 266,905 $ 248,598 Accumulated amortization (100,805 ) (101,917 ) Deferred leasing costs, net 166,100 146,681 Above-market operating leases 2,836 4,199 Accumulated amortization (2,150 ) (3,068 ) Above-market operating leases, net 686 1,131 In-place leases 66,526 82,097 Accumulated amortization (36,174 ) (46,625 ) In-place leases, net 30,352 35,472 Below-market ground lease obligation 490 490 Accumulated amortization (54 ) (46 ) Below-market ground lease obligation, net 436 444 Total deferred leasing costs and acquisition-related intangible assets, net $ 197,574 $ 183,728 Acquisition-related Intangible Liabilities, net: (1) Below-market operating leases $ 53,523 $ 65,440 Accumulated amortization (29,978 ) (40,495 ) Below-market operating leases, net 23,545 24,945 Above-market ground lease obligation 6,320 6,320 Accumulated amortization (727 ) (626 ) Above-market ground lease obligation, net 5,593 5,694 Total acquisition-related intangible liabilities, net $ 29,138 $ 30,639 _______________ (1) Included in deferred revenue and acquisition-related intangible liabilities, net in the consolidated balance sheets.
Amortization for the period related to deferred leasing costs and acquisition-related intangibles	The following table sets forth amortization related to deferred leasing costs and acquisition-related intangibles for the years ended December 31, 2018 , 2017 and 2016 . Year Ended December 31, 2018 2017 2016 (in thousands) Deferred leasing costs (1) $ 34,341 $ 31,675 $ 28,639 Above-market operating leases (2) 444 2,240 1,509 In-place leases (1) 15,915 18,650 11,676 Below-market ground lease obligation (3) 8 8 8 Below-market operating leases (4) (10,192 ) (10,768 ) (8,674 ) Above-market ground lease obligation (5) (101 ) (101 ) (101 ) Total $ 40,415 $ 41,704 $ 33,057 _______________ (1) The amortization of deferred leasing costs and in-place leases is recorded to depreciation and amortization expense and the amortization of lease incentives is recorded as a reduction to rental income in the consolidated statements of operations for the periods presented. (2) The amortization of above-market operating leases is recorded as a decrease to rental income in the consolidated statements of operations for the periods presented. (3) The amortization of the below-market ground lease obligation is recorded as an increase to ground lease expense in the consolidated statements of operations for the periods presented. (4) The amortization of below-market operating leases is recorded as an increase to rental income in the consolidated statements of operations for the periods presented. (5) The amortization of the above-market ground lease obligation is recorded as a decrease to ground lease expense in the consolidated statements of operations for the periods presented.
Estimated annual amortization related to deferred leasing costs and acquisition-related intangibles	The following table sets forth the estimated annual amortization expense related to deferred leasing costs and acquisition-related intangibles as of December 31, 2018 for future periods: Year Deferred Leasing Costs Above-Market Operating Leases (1) In-Place Leases Below-Market Ground Lease Obligation (2) Below-Market Operating Leases (3) Above-Market Ground Lease Obligation (4) (in thousands) 2019 31,980 192 16,675 8 (7,779 ) (100 ) 2020 26,868 38 5,963 8 (4,621 ) (100 ) 2021 21,787 38 2,861 8 (1,938 ) (100 ) 2022 18,683 38 1,589 8 (1,486 ) (100 ) 2023 14,914 38 648 8 (988 ) (100 ) Thereafter 51,868 342 2,616 396 (6,733 ) (5,093 ) Total $ 166,100 $ 686 $ 30,352 $ 436 $ (23,545 ) $ (5,593 ) _______________ (1) Represents estimated annual amortization related to above-market operating leases. Amounts will be recorded as a decrease to rental income in the consolidated statements of operations. (2) Represents estimated annual amortization related to below-market ground lease obligations. Amounts will be recorded as an increase to ground lease expense in the consolidated statements of operations. (3) Represents estimated annual amortization related to below-market operating leases. Amounts will be recorded as an increase to rental income in the consolidated statements of operations. (4) Represents estimated annual amortization related to above-market ground lease obligations. Amounts will be recorded as a decrease to ground lease expense in the consolidated statements of operations.

Receivables (Tables)

Receivables (Tables)	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Current receivables, net	Current receivables, net is primarily comprised of contractual rents and other lease-related obligations due from tenants. The balance consisted of the following as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Current receivables $ 24,815 $ 19,235 Allowance for uncollectible tenant receivables (4,639 ) (2,309 ) Current receivables, net $ 20,176 $ 16,926
Deferred rent receivables, net	Deferred rent receivables, net consisted of the following as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Deferred rent receivables $ 270,346 $ 249,629 Allowance for deferred rent receivables (3,339 ) (3,238 ) Deferred rent receivables, net $ 267,007 $ 246,391

Prepaid Expenses and Other As_2

Prepaid Expenses and Other Assets, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses and other assets, net	Prepaid expenses and other assets, net consisted of the following at December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Furniture, fixtures and other long-lived assets, net $ 36,833 $ 39,686 Notes receivable (1) 2,113 19,912 Prepaid expenses & acquisition deposits 13,927 55,108 Total Prepaid Expenses and Other Assets, Net $ 52,873 $ 114,706 _______________ (1) During the year ended December 31, 2018 , a note receivable with a balance of $15.1 million was repaid to the Company. Notes receivable are shown net of a valuation allowance of approximately $2.9 million as of December 31, 2018 .

Secured and Unsecured Debt of_3

Secured and Unsecured Debt of the Operating Partnership (Tables) - Kilroy Realty L.P. [Member]	12 Months Ended
	Dec. 31, 2018
Debt Instrument [Line Items]
Schedule of unsecured revolving credit facility	The following table summarizes the balance and terms of our unsecured revolving credit facility as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Outstanding borrowings $ 45,000 $ — Remaining borrowing capacity 705,000 750,000 Total borrowing capacity (1) $ 750,000 $ 750,000 Interest rate (2) 3.48 % 2.56 % Facility fee-annual rate (3) 0.200% Maturity date July 2022 _______________ (1) We may elect to borrow, subject to bank approval and obtaining commitments for any additional borrowing capacity, up to an additional $600.0 million under an accordion feature under the terms of the unsecured revolving credit facility and unsecured term loan facility. (2) Our unsecured revolving credit facility interest rate was calculated based on the contractual rate of LIBOR plus 1.000% as of December 31, 2018 and 2017 . (3) Our facility fee is paid on a quarterly basis and is calculated based on the total borrowing capacity. In addition to the facility fee, we incurred debt origination and legal costs. As of December 31, 2018 and 2017 , $4.7 million and $6.0 million of unamortized deferred financing costs, respectively, which are included in prepaid expenses and other assets, net on our consolidated balance sheets, remained to be amortized through the maturity date of our unsecured revolving credit facility.
Schedule of term loan facility	The following table summarizes the balance and terms of our unsecured term loan facility as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Outstanding borrowings $ 150,000 $ — Remaining borrowing capacity — 150,000 Total borrowing capacity (1) $ 150,000 $ 150,000 Interest rate (2) 3.49 % 2.66 % Undrawn facility fee-annual rate (3) 0.200% Maturity date July 2022 _______________ (1) As of December 31, 2018 and 2017 , $0.9 million and $1.2 million of unamortized deferred financing costs, respectively, remained to be amortized through the maturity date of our unsecured term loan facility. (2) Our unsecured term loan facility interest rate was calculated based on the contractual rate of LIBOR plus 1.100% as of December 31, 2018 and 2017 . (3) Prior to borrowing the full capacity of our unsecured term loan facility, the undrawn facility fee was calculated based on any unused borrowing capacity and was paid on a quarterly basis.
Stated debt maturities and scheduled amortization payments, excluding debt discounts	The following table summarizes the stated debt maturities and scheduled amortization payments as of December 31, 2018 : Year (in thousands) 2019 $ 76,309 2020 5,137 2021 5,342 2022 200,554 2023 305,775 Thereafter 2,362,694 Total aggregate principal value (1) $ 2,955,811 ________________________ (1) Includes gross principal balance of outstanding debt before the effect of the following at December 31, 2018 : $17.4 million of unamortized deferred financing costs for the unsecured term loan facility, unsecured senior notes and secured debt, $6.6 million of unamortized discounts for the unsecured senior notes and $0.8 million of unamortized premiums for the secured debt.
Capitalized interest and loan fees	The following table sets forth gross interest expense, including debt discount/premium and deferred financing cost amortization, net of capitalized interest, for the years ended 2018 , 2017 and 2016 . The interest expense capitalized was recorded as a cost of development and increased the carrying value of undeveloped land and construction in progress. Year Ended December 31, 2018 2017 2016 (in thousands) Gross interest expense $ 117,789 $ 112,577 $ 105,263 Capitalized interest and deferred financing costs (68,068 ) (46,537 ) (49,460 ) Interest expense $ 49,721 $ 66,040 $ 55,803
Secured debt [Member]
Debt Instrument [Line Items]
Debt balance and significant terms	The following table sets forth the composition of our secured debt as of December 31, 2018 and 2017 : Annual Stated Interest Rate (1) GAAP Effective Rate (1)(2) Maturity Date December 31, Type of Debt 2018 2017 (in thousands) Mortgage note payable 3.57% 3.57% December 2026 $ 170,000 $ 170,000 Mortgage note payable (3) 4.48% 4.48% July 2027 91,332 93,081 Mortgage note payable (3)(4) 6.05% 3.50% June 2019 75,238 78,894 Total secured debt $ 336,570 $ 341,975 Unamortized Deferred Financing Costs (1,039 ) (1,175 ) Total secured debt, net $ 335,531 $ 340,800 ______________ (1) All interest rates presented are fixed-rate interest rates. (2) Represents the effective interest rate including the amortization of initial issuance discounts/premiums excluding the amortization of deferred financing costs. (3) The secured debt and the related properties that secure the debt are held in a special purpose entity and the properties are not available to satisfy the debts and other obligations of the Company or the Operating Partnership. (4) As of December 31, 2018 and 2017 , the mortgage loan had unamortized debt premiums of $0.8 million and $2.6 million , respectively. In February 2019, the Company repaid this mortgage note payable at par.
Unsecured senior notes [Member]
Debt Instrument [Line Items]
Debt balance and significant terms	The following table summarizes the balance and significant terms of the registered unsecured senior notes issued by the Operating Partnership and outstanding, including unamortized discounts of $6.6 million and $6.3 million and unamortized deferred financing costs of $15.4 million and $12.5 million as of December 31, 2018 and 2017 , respectively: Net Carrying Amount Issuance date Maturity date Stated coupon rate Effective interest rate (1) 2018 2017 (in thousands) 4.750% Unsecured Senior Notes (2) November 2018 December 2028 4.750% 4.800% $ 400,000 $ — Unamortized discount and deferred financing costs (4,960 ) — Net carrying amount $ 395,040 $ — 4.350% Unsecured Senior Notes (3) October 2018 October 2026 4.350% 4.350% $ 200,000 $ — Unamortized discount and deferred financing costs (1,375 ) — Net carrying amount $ 198,625 $ — 4.300% Unsecured Senior Notes (3) July 2018 July 2026 4.300% 4.300% $ 50,000 $ — Unamortized discount and deferred financing costs (342 ) — Net carrying amount $ 49,658 $ — 3.450% Unsecured Senior Notes (4) December 2017 December 2024 3.450% 3.470% $ 425,000 $ 425,000 Unamortized discount and deferred financing costs (3,493 ) (4,047 ) Net carrying amount $ 421,507 $ 420,953 3.450% Unsecured Senior Notes (5) February 2017 February 2029 3.450% 3.450% $ 75,000 $ 75,000 Unamortized discount and deferred financing costs (432 ) (475 ) Net carrying amount $ 74,568 $ 74,525 3.350% Unsecured Senior Notes (5) February 2017 February 2027 3.350% 3.350% $ 175,000 $ 175,000 Unamortized discount and deferred financing costs (941 ) (1,056 ) Net carrying amount $ 174,059 $ 173,944 4.375% Unsecured Senior Notes (6) September 2015 October 2025 4.375% 4.444% $ 400,000 $ 400,000 Unamortized discount and deferred financing costs (3,738 ) (4,292 ) Net carrying amount $ 396,262 $ 395,708 4.250% Unsecured Senior Notes (7) July 2014 August 2029 4.250% 4.350% $ 400,000 $ 400,000 Unamortized discount and deferred financing costs (5,632 ) (6,164 ) Net carrying amount $ 394,368 $ 393,836 3.800% Unsecured Senior Notes (8) January 2013 January 2023 3.800% 3.800% $ 300,000 $ 300,000 Unamortized discount and deferred financing costs (1,108 ) (1,382 ) Net carrying amount $ 298,892 $ 298,618 6.625% Unsecured Senior Notes (9) May 2010 June 2020 6.625% 6.744% $ — $ 250,000 Unamortized discount and deferred financing costs — (1,321 ) Net carrying amount $ — $ 248,679 Total Unsecured Senior Notes, Net $ 2,402,979 $ 2,006,263 ________________________ (1) Represents the effective interest rate including the amortization of initial issuance discounts, excluding the amortization of deferred financing costs. (2) Interest on these notes is payable semi-annually in arrears on June 15th and December 15th of each year, beginning on June 15, 2019. (3) Interest on these notes is payable semi-annually in arrears on April 18th and October 18th of each year, beginning in April 18, 2019. (4) Interest on these notes is payable semi-annually in arrears on June 15th and December 15th of each year. (5) Interest on these notes is payable semi-annually in arrears on February 17th and August 17th of each year. (6) Interest on these notes is payable semi-annually in arrears on April 1st and October 1st of each year. (7) Interest on these notes is payable semi-annually in arrears on February 15th and August 15th of each year. (8) Interest on these notes is payable semi-annually in arrears on January 15th and July 15th of each year. (9) Interest on these notes is payable semi-annually in arrears on June 1st and December 1st of each year.

Deferred Revenue and Acquisit_2

Deferred Revenue and Acquisition Related Liabilities, net (Tables)	12 Months Ended
	Dec. 31, 2018
Deferred Revenue Disclosure [Abstract]
Deferred revenue and acquisition-related liabilities	Deferred revenue and acquisition-related intangible liabilities, net consisted of the following at December 31, 2018 and 2017 : December 31, 2018 2017 (in thousands) Deferred revenue related to tenant-funded tenant improvements $ 104,558 $ 104,260 Other deferred revenue 15,950 10,991 Acquisition-related intangible liabilities, net (1) 29,138 30,639 Total $ 149,646 $ 145,890 ________________________ (1) See Note 5 “Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, net” for additional information regarding our acquisition-related intangible liabilities.
Estimated amortization of deferred revenue related to tenant-funded improvements	The following is the estimated amortization of deferred revenue related to tenant-funded tenant improvements as of December 31, 2018 for the next five years and thereafter: Year Ending (in thousands) 2019 $ 16,973 2020 16,265 2021 14,612 2022 13,603 2023 11,857 Thereafter 31,248 Total $ 104,558

Stockholders' Equity of the C_2

Stockholders' Equity of the Company (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of common stock sales under the at-the-market offering	The following table sets forth information regarding sales of our common stock under our at-the-market offering programs for the years ended December 31, 2018 , 2017 and 2016 : Year Ended December 31, 2018 2017 2016 (in millions, except share data) Shares of common stock sold during the period 1,817,195 235,077 451,398 Weighted average price per share of common stock $ 73.64 $ 75.40 $ 71.50 Aggregate gross proceeds $ 133.8 $ 17.7 $ 32.3 Aggregate net proceeds after selling commissions $ 132.1 $ 17.5 $ 31.9
Schedule of accrued dividends and distributions	The following tables summarize accrued dividends and distributions for the noted outstanding shares of common stock and noncontrolling units as of December 31, 2018 and 2017 : December 31, 2018 2017 (in thousands) Dividends and Distributions payable to: Common stockholders $ 45,840 $ 41,914 Noncontrolling common unitholders of the Operating Partnership 922 883 RSU holders (1) 797 651 Total accrued dividends and distribution to common stockholders and noncontrolling unitholders $ 47,559 $ 43,448 ______________________ (1) The amount includes the value of the dividend equivalents that will be paid with additional RSUs (see Note 15 “Share-Based Compensation” for additional information).
Schedule of outstanding shares of common stock, preferred stock and noncontrolling units	December 31, 2018 2017 Outstanding Shares and Units: Common stock (1) 100,746,988 98,620,333 Noncontrolling common units 2,025,287 2,077,193 RSUs (2) 1,711,628 1,488,724 ______________________ (1) The amount includes nonvested shares. (2) The amount includes nonvested RSUs. Does not include 1,018,337 and 665,110 market measure-based RSUs because not all the necessary performance conditions have been met as of December 31, 2018 and 2017 , respectively. Refer to Note 15 “Share-Based Compensation” for additional information.

Preferred and Common Units of t

Preferred and Common Units of the Operating Partnership (Tables)	12 Months Ended
	Dec. 31, 2018
Class of Stock [Line Items]
Schedule of common stock sales under the at-the-market offering	The following table sets forth information regarding sales of our common stock under our at-the-market offering programs for the years ended December 31, 2018 , 2017 and 2016 : Year Ended December 31, 2018 2017 2016 (in millions, except share data) Shares of common stock sold during the period 1,817,195 235,077 451,398 Weighted average price per share of common stock $ 73.64 $ 75.40 $ 71.50 Aggregate gross proceeds $ 133.8 $ 17.7 $ 32.3 Aggregate net proceeds after selling commissions $ 132.1 $ 17.5 $ 31.9
Redeemable noncontrolling interest	The following table sets forth the number of common units held by the Company and the number of common units held by non-affiliated investors and certain of our executive officers and directors in the form of noncontrolling common units as well as the ownership interest held on each respective date: December 31, 2018 December 31, 2017 Company owned common units in the Operating Partnership 100,746,988 98,620,333 Company owned general partnership interest 98.0 % 97.9 % Noncontrolling common units of the Operating Partnership 2,025,287 2,077,193 Ownership interest of noncontrolling interest 2.0 % 2.1 %
Schedule of accrued dividends and distributions	The following tables summarize accrued dividends and distributions for the noted outstanding shares of common stock and noncontrolling units as of December 31, 2018 and 2017 : December 31, 2018 2017 (in thousands) Dividends and Distributions payable to: Common stockholders $ 45,840 $ 41,914 Noncontrolling common unitholders of the Operating Partnership 922 883 RSU holders (1) 797 651 Total accrued dividends and distribution to common stockholders and noncontrolling unitholders $ 47,559 $ 43,448 ______________________ (1) The amount includes the value of the dividend equivalents that will be paid with additional RSUs (see Note 15 “Share-Based Compensation” for additional information).
Schedule of outstanding shares of common stock, preferred stock and noncontrolling units	December 31, 2018 2017 Outstanding Shares and Units: Common stock (1) 100,746,988 98,620,333 Noncontrolling common units 2,025,287 2,077,193 RSUs (2) 1,711,628 1,488,724 ______________________ (1) The amount includes nonvested shares. (2) The amount includes nonvested RSUs. Does not include 1,018,337 and 665,110 market measure-based RSUs because not all the necessary performance conditions have been met as of December 31, 2018 and 2017 , respectively. Refer to Note 15 “Share-Based Compensation” for additional information.
Kilroy Realty L.P. [Member]
Class of Stock [Line Items]
Schedule of common stock sales under the at-the-market offering	During the years ended December 31, 2018 , 2017 and 2016 , the Company utilized its at-the-market stock offering programs to issue shares of common stock (see Note 13 “Stockholders’ Equity of the Company” for additional information). The net offering proceeds and property acquired using net offering proceeds contributed by the Company to the Operating Partnership in exchange for common units for the years ended December 31, 2018 , 2017 and 2016 are as follows: Year Ended December 31, 2018 2017 2016 (in millions, except share and per share data) Shares of common stock contributed by the Company 1,817,195 235,077 451,398 Common units exchanged for shares of common stock by the Company 1,817,195 235,077 451,398 Aggregate gross proceeds $ 133.8 $ 17.7 $ 32.3 Aggregate net proceeds after selling commissions $ 132.1 $ 17.5 $ 31.9
Schedule of accrued dividends and distributions	The following tables summarize accrued distributions for the noted common units as of December 31, 2018 and 2017 : December 31, 2018 December 31, 2017 (in thousands) Distributions payable to: General partner $ 45,840 $ 41,914 Common limited partners 922 883 RSU holders (1) 797 651 Total accrued distributions to common unitholders $ 47,559 $ 43,448 ______________________ (1) The amount includes the value of the dividend equivalents that will be paid with additional RSUs (see Note 15 “Share-Based Compensation” for additional information).
Schedule of outstanding shares of common stock, preferred stock and noncontrolling units	December 31, 2018 December 31, 2017 Outstanding Units: Common units held by the general partner 100,746,988 98,620,333 Common units held by the limited partners 2,025,287 2,077,193 RSUs (1) 1,711,628 1,488,724 ______________________ (1) Does not include 1,018,337 and 665,110 market measure-based RSUs because not all the necessary performance conditions have been met as of December 31, 2018 and 2017 , respectively. Refer to Note 15 “Share-Based Compensation” for additional information.

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Restricted Stock Units Valuation Assumptions	The total fair value of the Time-Based RSUs is based on the Company's closing share price on the NYSE on the respective fair valuation dates as detailed in the table below: December 2018 Time-Based RSU Grant 2018 Time-Based RSU Grant (1) 2017 Time-Based RSU Grant (2) 2016 Time-Based RSU Grant Service vesting period December 27, 2018 - January 5, 2023 January & February 2018 - January 5, 2021 February 2017 - January 5, 2020 January 28, 2016 - January 5, 2019 Fair value on valuation date (in millions) $ 18.5 $ 8.4 $ 7.5 $ 7.1 Fair value per share $ 62.00 $ 70.37 $ 73.30 $ 56.23 Date of fair valuation December 27, 2018 January & February 2018 February 2017 January 28, 2016 _______________ (1) The 2018 Time-Based RSUs consist of 56,015 RSUs granted on January 29, 2018 at a fair value per share of $70.37 and 67,818 RSUs granted on February 14, 2018 at a fair value per share of $66.46 . (2) The 2017 Time-Based RSUs consist of 41,119 RSUs granted on February 3, 2017 at a fair value per share of $73.30 and 57,901 RSUs granted on February 24, 2017 at a fair value per share of $77.16 . As of December 31, 2018 , the estimated number of RSUs earned for the 2018 and 2017 Performance-Based RSUs and the actual number of RSUs earned for the 2016 Performance-Based RSUs was as follows: 2018 Performance-Based RSUs 2017 Performance-Based RSUs 2016 Performance-Based RSUs Service vesting period February 14, 2018 - January, 2021 February 24, 2017 - January, 2020 January 28, 2016 - January, 2019 Target RSUs granted 158,205 130,956 168,077 Estimated RSUs earned (1) 254,235 170,994 241,438 Date of valuation February 14, 2018 February 24, 2017 January 28, 2016 _______________ (1) Estimated RSUs earned for the 2018 Performance-Based RSUs are based on the actual achievement of the 2018 FFO Performance Condition and assumes target level achievement of the 2018 Debt to EBITDA Ratio Performance Condition and the 2018 Market Condition. Estimated RSUs earned for the 2017 Performance-Based RSUs are based on the actual achievement of the 2017 FFO Performance Condition and assume target level achievement of the 2017 Market Condition and Other 2017 Performance Conditions. The 2016 Performance-Based RSUs earned are based on actual performance of the 2016 Performance Condition and the 2016 Market Condition.
Summary of Nonvested Restricted Stock	A summary of our nonvested restricted stock activity from January 1, 2018 through December 31, 2018 is presented below: Nonvested Weighted-Average Outstanding at January 1, 2018 22,884 $ 55.23 Transferred from time-based RSUs — — Vested (1) (22,884 ) 55.23 Outstanding as of December 31, 2018 — $ — _______________ (1) The total shares vested includes 9,637 shares that were tendered in accordance with the terms of the 2006 Plan to satisfy minimum statutory tax withholding requirements related to the restricted shares that have vested. We accept the return of shares at the current quoted closing share price of the Company’s common stock to satisfy tax withholding obligations
Summary of Nonvested and Vested Restricted Stock Activity	A summary of our nonvested and vested restricted stock activity for years ended December 31, 2018 , 2017 and 2016 is presented below: Shares Granted Shares Vested Years ended December 31, Nonvested Shares Issued Weighted-Average Grant Date Fair Value Per Share Vested Shares Total Fair Value at Vest Date (1) (in thousands) 2018 — $ — (22,884 ) $ 1,652 2017 — — (24,261 ) 1,781 2016 — — (24,262 ) 1,527 _______________ (1) Total fair value of shares vested was calculated based on the quoted closing share price of the Company’s common stock on the NYSE on the date of vesting.
Market measure-based Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Restricted Stock Units Award Activity	A summary of our performance and market-measure based RSU activity from January 1, 2018 through December 31, 2018 is presented below: Nonvested RSUs Vested RSUs Total RSUs Amount Weighted-Average (1) Outstanding at January 1, 2018 665,110 $ 68.83 55,672 720,782 Granted 601,012 68.51 1,067 602,079 Vested (261,875 ) 74.25 261,875 — Settled (2) (285,818 ) (285,818 ) Issuance of dividend equivalents (3) 14,090 71.75 2,976 17,066 Forfeited — (11 ) (11 ) Outstanding as of December 31, 2018 (4) 1,018,337 $ 67.29 35,761 1,054,098 _______________ (1) Represents the grant-date fair value for all awards, excluding the 2014 Performance-Based RSU Grant, which was re-measured upon stockholder approval of the amended 2006 Plan on May 22, 2014, as an insufficient number of shares were available to settle these RSUs upon initial grant on January 29, 2014. (2) Represents vested RSUs that were settled in shares of the Company’s common stock. Total shares settled include 139,933 shares that were tendered in accordance with the terms of the 2006 Plan to satisfy minimum statutory tax withholding requirements related to the RSUs settled. We accept the return of RSUs at the current quoted closing share price of the Company’s common stock to satisfy tax obligations. (3) Represents the issuance of dividend equivalents earned on the underlying RSUs. The dividend equivalents vest based on terms specified under the related RSU award agreement. (4) Outstanding RSUs as of December 31, 2018 represent the actual achievement of the FFO performance conditions and assumes target levels for the market and other performance conditions. The number of restricted stock units ultimately earned is subject to change based upon actual performance over the three-year vesting period. Dividend equivalents earned will vest along with the underlying award and are also subject to changes based on the number of RSUs ultimately earned for each underlying award. A summary of our performance and market-measure based RSU activity for years ended December 31, 2018 , 2017 and 2016 is presented below: RSUs Granted RSUs Vested Years ended December 31, Non-Vested RSUs Granted (1) Weighted-Average Fair Value Per Share (2) Vested RSUs Total Vest-Date Fair Value (in thousands) 2018 601,012 $ 68.51 (265,918 ) $ 18,906 2017 170,994 78.97 (194,991 ) 14,270 2016 258,393 57.36 (36,914 ) 2,788 _______________ (1) Non-vested RSUs granted during the years ended December 31, 2018 and 2017 are based on the actual achievement of the FFO performance conditions and assumes target level achievement for the market and other performance conditions. Non-vested RSUs granted during the year ended December 31, 2016 are based on the final performance of both the 2016 Performance and Market Conditions, and are non-vested as of December 31, 2018 as they were subject to the Compensation Committee’s confirmation of final performance. (2) Represents the grant-date fair value for all awards, excluding the 2014 Performance-Based RSU Grant, which was re-measured upon stockholder approval of the amended 2006 Plan on May 22, 2014, as an insufficient number of shares were available to settle these RSUs upon initial grant on January 29, 2014.
Time-Based Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Restricted Stock Units Award Activity	A summary of our time-based RSU activity for the years ended December 31, 2018 , 2017 and 2016 is presented below: RSUs Granted RSUs Vested Year ended December 31, Non-Vested RSUs Issued Weighted-Average Grant Date Fair Value Per Share Vested RSUs Total Vest-Date Fair Value (1) (in thousands) 2018 437,216 $ 64.21 (214,131 ) $ 14,768 2017 142,101 74.91 (228,095 ) 16,735 2016 173,747 58.29 (130,784 ) 8,438 _______________ (1) Total fair value of RSUs vested was calculated based on the quoted closing share price of the Company’s common stock on the NYSE on the day of vesting. Excludes the issuance of dividend equivalents earned on the underlying RSUs. The dividend equivalents vest based on terms specified under the related RSU award agreement. A summary of our time-based RSU activity from January 1, 2018 through December 31, 2018 is presented below: Nonvested RSUs Vested RSUs Total RSUs Amount Weighted Average Fair Value (1) Outstanding at January 1, 2018 331,546 $ 66.83 1,080,928 1,412,474 Granted 437,216 64.21 — 437,216 Vested (187,209 ) 63.85 187,209 — Settled (2) (202,536 ) (202,536 ) Issuance of dividend equivalents (3) 6,316 71.75 26,922 33,238 Forfeited (1,090 ) 70.62 — (1,090 ) Canceled (4) (3,435 ) (3,435 ) Outstanding as of December 31, 2018 586,779 $ 65.87 1,089,088 1,675,867 _______________ (1) Represents the grant-date fair value for all awards, excluding the 2014 Performance-Based RSU Grant, which was re-measured upon stockholder approval of the amended 2006 Plan on May 22, 2014, as an insufficient number of shares were available to settle these RSUs upon initial grant on January 29, 2014. (2) Represents vested RSUs that were settled in shares of the Company’s common stock. Total shares settled include 85,598 shares that were tendered in accordance with the terms of the 2006 Plan to satisfy minimum statutory tax withholding requirements related to the RSUs settled. We accept the return of RSUs at the current quoted closing share price of the Company’s common stock to satisfy tax obligations. (3) Represents the issuance of dividend equivalents earned on the underlying RSUs. The dividend equivalents vest based on terms specified under the related RSU award agreement. (4) For shares vested but not yet settled, we accept the return of RSUs at the current quoted closing share price of the Company’s common stock to satisfy minimum statutory tax-withholding requirements related to either the settlement or vesting of RSUs in accordance with the terms of the 2006 Plan.
December 2018 Market-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assumptions Utilized in the Monte Carlo Simulation Pricing Models	The following table summarizes the assumptions utilized in the Monte Carlo simulation pricing models: December 2018 Market-Based RSU Award Fair Value Assumptions Valuation date December 27, 2018 Fair value per share on valuation date $68.66 Expected share price volatility 23.0% Risk-free interest rate 2.4%
2018, 2017, and 2016 Performance-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assumptions Utilized in the Monte Carlo Simulation Pricing Models	The following table summarizes the assumptions utilized in the Monte Carlo simulation pricing models: 2018 Award Fair Value Assumptions 2017 Award Fair Value Assumptions 2016 Award Fair Value Assumptions Valuation date February 14, 2018 February 24, 2017 January 28, 2016 Fair value per share on valuation date $70.08 $80.89 $57.08 Expected share price volatility 20.00% 21.00% 26.00% Risk-free interest rate 2.37% 1.39% 1.13%

Future Minimum Rent (Tables)

Future Minimum Rent (Tables)	12 Months Ended
	Dec. 31, 2018
Leases [Abstract]
Future contractual minimum rent under operating lease	Future contractual minimum rent under operating leases as of December 31, 2018 for future periods is summarized as follows: Year Ending (in thousands) 2019 $ 566,783 2020 632,875 2021 631,835 2022 620,684 2023 586,371 Thereafter 3,240,143 Total (1) $ 6,278,691 ______________ (1) Excludes residential leases and leases with a term of one year or less. The minimum commitment under our ground leases as of December 31, 2018 for five years and thereafter is as follows: Year Ending (in thousands) 2019 $ 5,154 2020 5,154 2021 5,154 2022 5,154 2023 5,154 Thereafter 233,619 Total (1)(2)(3)(4)(5) $ 259,389 ________________________ (1) Excludes contingent future rent payments based on gross income or adjusted gross income and reflects the minimum ground lease obligations before the impact of ground lease extension options. (2) One of our ground lease obligations is subject to a fair market value adjustment every five years ; however, the lease includes ground rent subprotection and infrastructure rent credits which currently limit our annual rental obligations to $1.0 million . The contractual obligations for that ground lease included above assumes the lesser of $1.0 million or annual lease rental obligation in effect as of December 31, 2018 . (3) One of our ground lease obligations includes a component which is based on the percentage of gross income that exceeds the minimum ground rent. The minimum rent is subject to increases every five years based on 50% of the average annual percentage rent for the previous five years. The contractual obligations for that lease included above assume the current annual ground lease obligation in effect at December 31, 2018 for the remainder of the lease term since we cannot predict future adjustments. (4) One of our ground lease obligations is subject to a fair market value adjustment every five years based on a combination of CPI adjustments and third-party appraisals limited to maximum increases annually. The contractual obligations for that lease included above assume the current annual ground lease obligation in effect at December 31, 2018 for the remainder of the lease term since we cannot predict future adjustments. (5) One of our ground lease obligations includes a component which is based on the percentage of adjusted gross income that exceeds the minimum ground rent. The minimum rent is subject to increases every 10 years by an amount equal to 60% of the average annual percentage rent for the previous three years. The contractual obligations for this lease included above assume the current annual ground lease obligation in effect at December 31, 2018 for the remainder of the lease term since we cannot predict future adjustments.

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of contractual expiration dates for ground leases	The following table summarizes our properties that are held subject to long-term noncancellable ground lease obligations and the respective contractual expiration dates: Property Contractual Expiration Date (1) 601 108th Ave NE, Bellevue, WA November 2093 701, 801 and 837 N. 34th Street, Seattle, WA (2) December 2041 1701 Page Mill Road and 3150 Porter Drive, Palo Alto, CA December 2067 Kilroy Airport Center Phases I, II, and III, Long Beach, CA July 2084 ____________________ (1) Reflects the contractual expiration date prior to the impact of any extension or purchase options held by the Company. (2) The Company has three 10 -year and one 45 -year extension options for this ground lease, which if exercised would extend the expiration date to December 2116.
Schedule of future minimum rental repayments for ground leases	Future contractual minimum rent under operating leases as of December 31, 2018 for future periods is summarized as follows: Year Ending (in thousands) 2019 $ 566,783 2020 632,875 2021 631,835 2022 620,684 2023 586,371 Thereafter 3,240,143 Total (1) $ 6,278,691 ______________ (1) Excludes residential leases and leases with a term of one year or less. The minimum commitment under our ground leases as of December 31, 2018 for five years and thereafter is as follows: Year Ending (in thousands) 2019 $ 5,154 2020 5,154 2021 5,154 2022 5,154 2023 5,154 Thereafter 233,619 Total (1)(2)(3)(4)(5) $ 259,389 ________________________ (1) Excludes contingent future rent payments based on gross income or adjusted gross income and reflects the minimum ground lease obligations before the impact of ground lease extension options. (2) One of our ground lease obligations is subject to a fair market value adjustment every five years ; however, the lease includes ground rent subprotection and infrastructure rent credits which currently limit our annual rental obligations to $1.0 million . The contractual obligations for that ground lease included above assumes the lesser of $1.0 million or annual lease rental obligation in effect as of December 31, 2018 . (3) One of our ground lease obligations includes a component which is based on the percentage of gross income that exceeds the minimum ground rent. The minimum rent is subject to increases every five years based on 50% of the average annual percentage rent for the previous five years. The contractual obligations for that lease included above assume the current annual ground lease obligation in effect at December 31, 2018 for the remainder of the lease term since we cannot predict future adjustments. (4) One of our ground lease obligations is subject to a fair market value adjustment every five years based on a combination of CPI adjustments and third-party appraisals limited to maximum increases annually. The contractual obligations for that lease included above assume the current annual ground lease obligation in effect at December 31, 2018 for the remainder of the lease term since we cannot predict future adjustments. (5) One of our ground lease obligations includes a component which is based on the percentage of adjusted gross income that exceeds the minimum ground rent. The minimum rent is subject to increases every 10 years by an amount equal to 60% of the average annual percentage rent for the previous three years. The contractual obligations for this lease included above assume the current annual ground lease obligation in effect at December 31, 2018 for the remainder of the lease term since we cannot predict future adjustments.

Fair Value Measurements and D_2

Fair Value Measurements and Disclosures (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair value of the company's marketable securities	The following table sets forth the fair value of our marketable securities as of December 31, 2018 and 2017 : Fair Value (Level 1) (1) 2018 2017 Description (in thousands) Marketable securities (2) $ 21,779 $ 20,674 _______________ (1) Based on quoted prices in active markets for identical securities. (2) The marketable securities are held in a limited rabbi trust .
Net (loss) gain on marketable securities	The following table sets forth the net (loss) gain on marketable securities recorded during the years ended December 31, 2018 , 2017 and 2016 : December 31, 2018 2017 2016 Description (in thousands) Net (loss) gain on marketable securities $ (1,851 ) $ 3,023 $ 1,130
Carrying value and fair value of other financial instruments	The following table sets forth the carrying value and the fair value of our other financial instruments as of December 31, 2018 and 2017 : December 31, 2018 2017 Carrying Value Fair Value (1) Carrying Value Fair Value (1) (in thousands) Liabilities Secured debt, net $ 335,531 $ 335,885 $ 340,800 $ 346,858 Unsecured debt, net 2,552,070 2,546,386 2,006,263 2,077,199 Unsecured line of credit (1) 45,000 45,058 — — _______________ (1) Fair value calculated using Level II inputs, which are based on model-derived valuations in which significant inputs and significant value drivers are observable in active markets.

Net Income Available to Commo_3

Net Income Available to Common Stockholders Per Share of the Company (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Net income available to common stockholders	The following table reconciles the numerator and denominator in computing the Company’s basic and diluted per-share computations for net income available to common stockholders for the years ended December 31, 2018 , 2017 and 2016 : Year Ended December 31, 2018 2017 2016 (in thousands, except unit and per unit amounts) Numerator: Net income attributable to Kilroy Realty Corporation $ 258,415 $ 164,612 $ 293,788 Total preferred dividends — (13,363 ) (13,250 ) Allocation to participating securities (1) (2,004 ) (1,975 ) (3,839 ) Numerator for basic and diluted net income available to common stockholders $ 256,411 $ 149,274 $ 276,699 Denominator: Basic weighted average vested shares outstanding 99,972,359 98,113,561 92,342,483 Effect of dilutive securities 510,006 613,770 680,551 Diluted weighted average vested shares and common stock equivalents outstanding 100,482,365 98,727,331 93,023,034 Basic earnings per share: Net income available to common stockholders per share $ 2.56 $ 1.52 $ 3.00 Diluted earnings per share: Net income available to common stockholders per share $ 2.55 $ 1.51 $ 2.97 ________________________ (1) Participating securities include nonvested shares, certain time-based RSUs and vested market measure-based RSUs.

Net Income Available to Commo_4

Net Income Available to Common Unitholders Per Unit of the Operating Partnership (Tables)	12 Months Ended
	Dec. 31, 2018
Net Income Available To Common Unitholders [Line Items]
Net income available to common unitholders	The following table reconciles the numerator and denominator in computing the Company’s basic and diluted per-share computations for net income available to common stockholders for the years ended December 31, 2018 , 2017 and 2016 : Year Ended December 31, 2018 2017 2016 (in thousands, except unit and per unit amounts) Numerator: Net income attributable to Kilroy Realty Corporation $ 258,415 $ 164,612 $ 293,788 Total preferred dividends — (13,363 ) (13,250 ) Allocation to participating securities (1) (2,004 ) (1,975 ) (3,839 ) Numerator for basic and diluted net income available to common stockholders $ 256,411 $ 149,274 $ 276,699 Denominator: Basic weighted average vested shares outstanding 99,972,359 98,113,561 92,342,483 Effect of dilutive securities 510,006 613,770 680,551 Diluted weighted average vested shares and common stock equivalents outstanding 100,482,365 98,727,331 93,023,034 Basic earnings per share: Net income available to common stockholders per share $ 2.56 $ 1.52 $ 3.00 Diluted earnings per share: Net income available to common stockholders per share $ 2.55 $ 1.51 $ 2.97 ________________________ (1) Participating securities include nonvested shares, certain time-based RSUs and vested market measure-based RSUs.
Kilroy Realty L.P. [Member]
Net Income Available To Common Unitholders [Line Items]
Net income available to common unitholders	The following table reconciles the numerator and denominator in computing the Operating Partnership’s basic and diluted per-unit computations for net income available to common unitholders for the years ended 2018 , 2017 and 2016 : Year Ended December 31, 2018 2017 2016 (in thousands, except unit and per unit amounts) Numerator: Net income attributable to Kilroy Realty, L.P. $ 263,210 $ 167,440 $ 300,063 Total preferred distributions — (13,363 ) (13,250 ) Allocation to participating securities (1) (2,004 ) (1,975 ) (3,839 ) Numerator for basic and diluted net income available to common unitholders $ 261,206 $ 152,102 $ 282,974 Denominator: Basic weighted average vested units outstanding 102,025,276 100,246,567 94,771,688 Effect of dilutive securities 510,006 613,770 680,551 Diluted weighted average vested units and common unit equivalents outstanding 102,535,282 100,860,337 95,452,239 Basic earnings per unit: Net income available to common unitholders per unit $ 2.56 $ 1.52 $ 2.99 Diluted earnings per unit: Net income available to common unitholders per unit $ 2.55 $ 1.51 $ 2.96 ________________________ (1) Participating securities include nonvested shares, certain time-based RSUs and vested market measure-based RSUs.

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information of the Company (Tables)	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Schedule of supplemental cash flows, company	Supplemental cash flow information follows (in thousands): Year Ended December 31, 2018 2017 2016 SUPPLEMENTAL CASH FLOWS INFORMATION: Cash paid for interest, net of capitalized interest of $65,627, $44,757, and $47,675 as of December 31, 2018, 2017 and 2016, respectively $ 44,697 $ 67,336 $ 54,295 NON-CASH INVESTING TRANSACTIONS: Accrual for expenditures for operating properties and development and redevelopment properties $ 158,626 $ 116,089 $ 62,589 Tenant improvements funded directly by tenants $ 13,968 $ 15,314 $ 18,050 Assumption of other assets and liabilities in connection with operating and development property acquisitions, net (Note 3) $ 40,624 $ 1,443 $ 5,863 Accrual for receivable related to development properties $ — $ — $ 1,350 NON-CASH FINANCING TRANSACTIONS: Accrual of dividends and distributions payable to common stockholders and common unitholders (Notes 13 and 28) $ 47,559 $ 43,448 $ 220,650 Exchange of common units of the Operating Partnership into shares of the Company’s common stock $ 1,962 $ 10,939 $ 8,893 Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders (Note 13) $ — $ — $ 1,656 Issuance of common units of the Operating Partnership in connection with an acquisition $ — $ — $ 48,033 Secured debt assumed by buyers in connection with land disposition (Note 4) $ — $ — $ 2,322 Supplemental cash flow information follows (in thousands): Year Ended December 31, 2018 2017 2016 SUPPLEMENTAL CASH FLOWS INFORMATION: Cash paid for interest, net of capitalized interest of $65,627, $44,757, and $47,675 as of December 31, 2018, 2017 and 2016, respectively $ 44,697 $ 67,336 $ 54,295 NON-CASH INVESTING TRANSACTIONS: Accrual for expenditures for operating properties and development and redevelopment properties $ 158,626 $ 116,089 $ 62,589 Tenant improvements funded directly by tenants $ 13,968 $ 15,314 $ 18,050 Assumption of other assets and liabilities in connection with operating and development property acquisitions, net (Note 3) $ 40,624 $ 1,443 $ 5,863 Accrual for receivable related to development properties $ — $ — $ 1,350 NON-CASH FINANCING TRANSACTIONS: Accrual of dividends and distributions payable to common stockholders and common $ 47,559 $ 43,448 $ 220,650 Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders (Note 14) $ — $ — $ 1,656 Issuance of common units in connection with a development property acquisition $ — $ — $ 48,033 Secured debt assumed by buyers in connection with land disposition (Note 4) $ — $ — $ 2,322
Reconciliation of cash and cash equivalents and restricted cash	The following is a reconciliation of our cash and cash equivalents and restricted cash at the beginning and end of the years ended 2018 , 2017 and 2016 . Year Ended December 31, 2018 2017 2016 RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH: Cash and cash equivalents at beginning of period $ 57,649 $ 193,418 $ 56,508 Restricted cash at beginning of period 9,149 56,711 696 Cash and cash equivalents and restricted cash at beginning of period $ 66,798 $ 250,129 $ 57,204 Cash and cash equivalents at end of period $ 51,604 $ 57,649 $ 193,418 Restricted cash at end of period 119,430 9,149 56,711 Cash and cash equivalents and restricted cash at end of period $ 171,034 $ 66,798 $ 250,129 The following is a reconciliation of our cash and cash equivalents and restricted cash at the beginning and end of the years ended 2018 , 2017 and 2016 . Year Ended December 31, 2018 2017 2016 RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH: Cash and cash equivalents at beginning of period $ 57,649 $ 193,418 $ 56,508 Restricted cash at beginning of period 9,149 56,711 696 Cash and cash equivalents and restricted cash at beginning of period $ 66,798 $ 250,129 $ 57,204 Cash and cash equivalents at end of period $ 51,604 $ 57,649 $ 193,418 Restricted cash at end of period 119,430 9,149 56,711 Cash and cash equivalents and restricted cash at end of period $ 171,034 $ 66,798 $ 250,129

Supplemental Cash Flow Elements

Supplemental Cash Flow Elements (Tables)	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Schedule of supplemental cash flows, operating unit	Supplemental cash flow information follows (in thousands): Year Ended December 31, 2018 2017 2016 SUPPLEMENTAL CASH FLOWS INFORMATION: Cash paid for interest, net of capitalized interest of $65,627, $44,757, and $47,675 as of December 31, 2018, 2017 and 2016, respectively $ 44,697 $ 67,336 $ 54,295 NON-CASH INVESTING TRANSACTIONS: Accrual for expenditures for operating properties and development and redevelopment properties $ 158,626 $ 116,089 $ 62,589 Tenant improvements funded directly by tenants $ 13,968 $ 15,314 $ 18,050 Assumption of other assets and liabilities in connection with operating and development property acquisitions, net (Note 3) $ 40,624 $ 1,443 $ 5,863 Accrual for receivable related to development properties $ — $ — $ 1,350 NON-CASH FINANCING TRANSACTIONS: Accrual of dividends and distributions payable to common stockholders and common unitholders (Notes 13 and 28) $ 47,559 $ 43,448 $ 220,650 Exchange of common units of the Operating Partnership into shares of the Company’s common stock $ 1,962 $ 10,939 $ 8,893 Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders (Note 13) $ — $ — $ 1,656 Issuance of common units of the Operating Partnership in connection with an acquisition $ — $ — $ 48,033 Secured debt assumed by buyers in connection with land disposition (Note 4) $ — $ — $ 2,322 Supplemental cash flow information follows (in thousands): Year Ended December 31, 2018 2017 2016 SUPPLEMENTAL CASH FLOWS INFORMATION: Cash paid for interest, net of capitalized interest of $65,627, $44,757, and $47,675 as of December 31, 2018, 2017 and 2016, respectively $ 44,697 $ 67,336 $ 54,295 NON-CASH INVESTING TRANSACTIONS: Accrual for expenditures for operating properties and development and redevelopment properties $ 158,626 $ 116,089 $ 62,589 Tenant improvements funded directly by tenants $ 13,968 $ 15,314 $ 18,050 Assumption of other assets and liabilities in connection with operating and development property acquisitions, net (Note 3) $ 40,624 $ 1,443 $ 5,863 Accrual for receivable related to development properties $ — $ — $ 1,350 NON-CASH FINANCING TRANSACTIONS: Accrual of dividends and distributions payable to common stockholders and common $ 47,559 $ 43,448 $ 220,650 Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders (Note 14) $ — $ — $ 1,656 Issuance of common units in connection with a development property acquisition $ — $ — $ 48,033 Secured debt assumed by buyers in connection with land disposition (Note 4) $ — $ — $ 2,322
Reconciliation of cash and cash equivalents and restricted cash	The following is a reconciliation of our cash and cash equivalents and restricted cash at the beginning and end of the years ended 2018 , 2017 and 2016 . Year Ended December 31, 2018 2017 2016 RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH: Cash and cash equivalents at beginning of period $ 57,649 $ 193,418 $ 56,508 Restricted cash at beginning of period 9,149 56,711 696 Cash and cash equivalents and restricted cash at beginning of period $ 66,798 $ 250,129 $ 57,204 Cash and cash equivalents at end of period $ 51,604 $ 57,649 $ 193,418 Restricted cash at end of period 119,430 9,149 56,711 Cash and cash equivalents and restricted cash at end of period $ 171,034 $ 66,798 $ 250,129 The following is a reconciliation of our cash and cash equivalents and restricted cash at the beginning and end of the years ended 2018 , 2017 and 2016 . Year Ended December 31, 2018 2017 2016 RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH: Cash and cash equivalents at beginning of period $ 57,649 $ 193,418 $ 56,508 Restricted cash at beginning of period 9,149 56,711 696 Cash and cash equivalents and restricted cash at beginning of period $ 66,798 $ 250,129 $ 57,204 Cash and cash equivalents at end of period $ 51,604 $ 57,649 $ 193,418 Restricted cash at end of period 119,430 9,149 56,711 Cash and cash equivalents and restricted cash at end of period $ 171,034 $ 66,798 $ 250,129

Tax Treatment of Distributions

Tax Treatment of Distributions (Tables)	12 Months Ended
	Dec. 31, 2018
Class of Stock [Line Items]
Reconciliation of dividends declared to dividends paid	The following table reconciles the dividends declared per share of common stock to the dividends paid per share of common stock during the years ended December 31, 2018 , 2017 and 2016 as follows: Year Ended December 31, Dividends 2018 2017 2016 Dividends declared per share of common stock $ 1.790 $ 1.650 $ 3.375 Less: Dividends declared in the current year and paid in the following year (0.455 ) (0.425 ) (2.275 ) Add: Dividends declared in the prior year and paid in the current year (1) 0.425 2.275 0.350 Dividends paid per share of common stock $ 1.760 $ 3.500 $ 1.450 _________________ (1) The fourth quarter 2016 dividend of $2.275 per share of common stock consists of a special cash dividend of $1.90 per share of common stock and a regular quarterly cash dividend of $0.375 per share of common stock. The $1.90 per share special distribution is treated as paid in two tax years for income tax purposes: $1.587 is treated as paid on December 31, 2016 and $0.313 is treated as paid on January 13, 2017. The $0.375 per share regular quarterly distribution is considered a 2017 dividend distribution for income tax purposes.
Common Stock [Member]
Class of Stock [Line Items]
Reconciliation of dividends declared to dividends paid	The unaudited income tax treatment for the dividends to common stockholders reportable for the years ended December 31, 2018 , 2017 and 2016 as identified in the table above was as follows: Year Ended December 31, Shares of Common Stock 2018 2017 2016 Ordinary income (1) $ 1.474 83.73 % $ 1.356 70.87 % $ 1.500 49.40 % Qualified dividend 0.003 0.19 0.002 0.11 0.002 0.06 Return of capital 0.275 15.64 0.344 18.00 — — Capital gains (2) 0.008 0.44 — — 1.212 39.89 Unrecaptured section 1250 gains — — 0.211 11.02 0.323 10.65 $ 1.760 100.00 % $ 1.913 100.00 % $ 3.037 100.00 % _________________ (1) The Tax Cuts and Jobs Act enacted on December 22, 2017 generally allows a deduction for noncorporate taxpayers equal to 20% of ordinary dividends distributed by a REIT (excluding capital gain dividends and qualified dividend income). The amount of dividend eligible for this deduction is referred to as the Section 199A Dividend. For the year ended December 31, 2018 , the Section 199A Dividend is equal to the total ordinary income dividend. (2) Capital gains are comprised entirely of 20% rate gains.
Series G Preferred Stock [Member]
Class of Stock [Line Items]
Reconciliation of dividends declared to dividends paid	The 6.875% Series G Cumulative Redeemable Preferred Stock was issued in March 2012 and redeemed in March 2017. The unaudited income tax treatment for the dividends to Series G preferred stockholders reportable for the years ended December 31, 2017 and 2016 was as follows: Year Ended December 31, Preferred Shares 2017 2016 Ordinary income $ 0.371 86.43 % $ 0.848 49.31 % Qualified dividend 0.001 0.14 0.001 0.06 Capital gains (1) — — 0.687 39.97 Unrecaptured section 1250 gains 0.058 13.43 0.183 10.66 $ 0.430 100.00 % $ 1.719 100.00 % __________________ (1) Capital gains are comprised entirely of 20% rate gains.
Series H Preferred Stock [Member]
Class of Stock [Line Items]
Reconciliation of dividends declared to dividends paid	The 6.375% Series H Cumulative Redeemable Preferred Stock was issued in August 2012 and redeemed in August 2017. The unaudited income tax treatment for the dividends to Series H preferred stockholders reportable for the years ended December 31, 2017 and 2016 was as follows: Year Ended December 31, Preferred Shares 2017 2016 Ordinary income $ 1.033 86.43 % $ 0.786 49.31 % Qualified dividend 0.002 0.14 0.001 0.06 Capital gains (1) — — 0.637 39.97 Unrecaptured section 1250 gains 0.160 13.43 0.170 10.66 $ 1.195 100.00 % $ 1.594 100.00 % __________________ (1) Capital gains are comprised entirely of 20% rate gains.

Quarterly Financial Informati_3

Quarterly Financial Information of the Company (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of summarized quarterly financial data	Summarized quarterly financial data for the years ended December 31, 2018 and 2017 was as follows: 2018 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per share amounts) Revenues $ 182,822 $ 187,072 $ 186,562 $ 190,842 Net income 40,971 31,755 38,310 166,890 Net income attributable to Kilroy Realty Corporation 36,246 27,549 34,400 160,220 Net income available to common stockholders 36,246 27,549 34,400 160,220 Net income available to common stockholders per share – basic 0.36 0.27 0.34 1.59 Net income available to common stockholders per share – diluted 0.36 0.27 0.33 1.58 2017 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per share amounts) Revenues $ 179,308 $ 180,598 $ 181,534 $ 177,561 Net income 37,281 35,306 75,488 32,540 Net income attributable to Kilroy Realty Corporation 33,525 31,448 71,110 28,529 Preferred dividends and distributions (7,196 ) (1,615 ) (4,552 ) — Net income available to common stockholders 26,329 29,833 66,558 28,529 Net income available to common stockholders per share – basic 0.27 0.30 0.67 0.28 Net income available to common stockholders per share – diluted 0.26 0.30 0.67 0.28 ____________________ (1) The summation of the quarterly financial data may not equal the annual number reported on the consolidated statements of operations due to rounding. For the year ended December 31, 2018 , the summation of the quarterly net income available to common stockholders per share does not equal the annual number reported on the consolidated statements of operations due to the Company’s at-the-market stock offering programs that occurred during the year.

Quarterly Financial Informati_4

Quarterly Financial Information of the Operating Partnership (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Schedule of summarized quarterly financial data	Summarized quarterly financial data for the years ended December 31, 2018 and 2017 was as follows: 2018 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per share amounts) Revenues $ 182,822 $ 187,072 $ 186,562 $ 190,842 Net income 40,971 31,755 38,310 166,890 Net income attributable to Kilroy Realty Corporation 36,246 27,549 34,400 160,220 Net income available to common stockholders 36,246 27,549 34,400 160,220 Net income available to common stockholders per share – basic 0.36 0.27 0.34 1.59 Net income available to common stockholders per share – diluted 0.36 0.27 0.33 1.58 2017 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per share amounts) Revenues $ 179,308 $ 180,598 $ 181,534 $ 177,561 Net income 37,281 35,306 75,488 32,540 Net income attributable to Kilroy Realty Corporation 33,525 31,448 71,110 28,529 Preferred dividends and distributions (7,196 ) (1,615 ) (4,552 ) — Net income available to common stockholders 26,329 29,833 66,558 28,529 Net income available to common stockholders per share – basic 0.27 0.30 0.67 0.28 Net income available to common stockholders per share – diluted 0.26 0.30 0.67 0.28 ____________________ (1) The summation of the quarterly financial data may not equal the annual number reported on the consolidated statements of operations due to rounding. For the year ended December 31, 2018 , the summation of the quarterly net income available to common stockholders per share does not equal the annual number reported on the consolidated statements of operations due to the Company’s at-the-market stock offering programs that occurred during the year.
Kilroy Realty L.P. [Member]
Schedule of summarized quarterly financial data	Summarized quarterly financial data for the years ended December 31, 2018 and 2017 was as follows: 2018 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per unit amounts) Revenues $ 182,822 $ 187,072 $ 186,562 $ 190,842 Net income 40,971 31,755 38,310 166,890 Net income attributable to the Operating Partnership 36,893 28,015 34,993 163,309 Net income available to common unitholders 36,893 28,015 34,993 163,309 Net income available to common unitholders per unit – basic 0.36 0.27 0.34 1.58 Net income available to common unitholders per unit – diluted 0.36 0.27 0.33 1.57 2017 Quarter Ended (1) March 31, June 30, September 30, December 31, (in thousands, except per unit amounts) Revenues $ 179,308 $ 180,598 $ 181,534 $ 177,561 Net income 37,281 35,306 75,488 32,540 Net income attributable to the Operating Partnership 34,054 31,971 72,402 29,013 Preferred distributions (7,196 ) (1,615 ) (4,552 ) — Net income available to common unitholders 26,858 30,356 67,850 29,013 Net income available to common unitholders per unit – basic 0.26 0.30 0.67 0.28 Net income available to common unitholders per unit – diluted 0.26 0.30 0.67 0.28 ___________________ (1) The summation of the quarterly financial data may not equal the annual number reported on the consolidated statements of operations due to rounding. For the year ended December 31, 2018 , the summation of the quarterly net income available to common stockholders per share does not equal the annual number reported on the consolidated statements of operations due to the Company’s at-the-market stock offering programs that occurred during the year

Organization and Ownership (Det

Organization and Ownership (Details) - Dec. 31, 2018	ft²	residential_unit	Total	project	tenant	building	property
Real Estate Properties [Line Items]
Rentable Square Feet (unaudited)	13,232,580
Office properties [Member]
Real Estate Properties [Line Items]
Number of buildings						94	4
Rentable Square Feet (unaudited)	13,232,580
Number of Tenants | tenant					482
Percentage Occupied (unaudited)			94.40%
Percentage Leased (unaudited)			96.60%
Stabilized residential properties [Member]
Real Estate Properties [Line Items]
Number of buildings | building						1
Percentage Occupied (unaudited)			79.70%
Number of units in real estate property | building						200
Development projects in lease-up [Member]
Real Estate Properties [Line Items]
Number of buildings | project				2
Rentable Square Feet (unaudited)	1,150,000
Development properties [Member]
Real Estate Properties [Line Items]
Number of buildings | project				3
Rentable Square Feet (unaudited)	1,290,000
Production, Distribution and Repair (PDR) [Member] | Development projects in lease-up [Member]
Real Estate Properties [Line Items]
Rentable Square Feet (unaudited)	88,000
Retail site [Member] | Development properties [Member]
Real Estate Properties [Line Items]
Rentable Square Feet (unaudited)	96,000
Number of residential units | residential_unit		801

Organization and Ownership - Na

Organization and Ownership - Narrative (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2018project	Dec. 31, 2018building	Dec. 31, 2018a	Dec. 31, 2018property	Dec. 31, 2017
Real Estate Properties [Line Items]
Stabilized occupancy	95.00%
Lease-up properties, maximum stabilized occupancy, duration	1 year
Ownership interest of noncontrolling interest		2.00%					2.10%
100 First LLC and 303 Second LLC [Member]
Real Estate Properties [Line Items]
Percentage of general partnership interest owned by the company in the Operating Partnership		56.00%
Redwood LLC [Member]
Real Estate Properties [Line Items]
Percentage of general partnership interest owned by the company in the Operating Partnership		93.00%
Washington [Member]
Real Estate Properties [Line Items]
Number of buildings						8
Washington - land parcel [Member]
Real Estate Properties [Line Items]
Number of buildings | building				1
Development sites [Member]
Real Estate Properties [Line Items]
Number of buildings | project			5
Office properties [Member]
Real Estate Properties [Line Items]
Number of buildings				94		4
Gross Site Acreage (unaudited) | a					73
Properties and Development Projects [Member]
Real Estate Properties [Line Items]
Property Ownership Percentage		100.00%
Development properties [Member]
Real Estate Properties [Line Items]
Number of buildings						3
Development properties [Member] | 100 First LLC and 303 Second LLC [Member]
Real Estate Properties [Line Items]
Number of buildings						2
Operating Partnership [Member]
Real Estate Properties [Line Items]
Percentage of general partnership interest owned by the company in the Operating Partnership		98.00%					97.90%
Kilroy Realty Finance, Inc. [Member]
Real Estate Properties [Line Items]
Percentage of general partnership interest owned by wholly-owned subsidiary of the Company		1.00%
Kilroy Realty L.P. [Member]
Real Estate Properties [Line Items]
Percentage of limited partnership interest owned by Operating Partnership		99.00%

Basis of Presentation and Sig_4

Basis of Presentation and Significant Accounting Policies - Narrative (Details)	Aug. 15, 2017	Mar. 30, 2017	Aug. 31, 2012	Mar. 31, 2012	Dec. 31, 2018USD ($)property_partnershipground_leasesegmentprojecttenantbuildingVIEproperty	Dec. 31, 2017USD ($)buildingVIE	Dec. 31, 2016USD ($)	Jan. 01, 2019USD ($)
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of VIEs | VIE					3	2
VIE asset amount					$ 615,400,000	$ 426,500,000
VIE, carrying amount, liabilities					45,100,000	27,300,000
Noncontrolling interest in consolidated subsidiary					192,363,000	181,575,000
Depreciation of real estate					$ 198,578,000	190,515,000	$ 171,983,000
Number of consolidated property partnerships | property_partnership					3
REIT annual taxable income distribution requirement percentage					90.00%
Company annual taxable income distribution					100.00%
Income tax provision					$ 0	0	0
Number of operating segments | segment					1
Net cash provided by (used in) investing activities					$ (808,915,000)	(359,102,000)	(579,420,000)
Initial premium on outstanding amount of secured debt					800,000
Original issuance costs of redeemed preferred units					0	7,589,000	0
Cash, FDIC insured amount					$ 250,000
Number of ground leases | ground_lease					4
Real estate investment [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
VIE asset amount					$ 543,900,000	$ 382,100,000
Properties held for sale [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of buildings | building					0	0
Minimum [Member] | Building and building improvements [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property depreciable lives						25 years
Minimum [Member] | Leasehold improvements [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property depreciable lives						1 year
Maximum [Member] | Building and building improvements [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property depreciable lives						40 years
Maximum [Member] | Leasehold improvements [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property depreciable lives						20 years
Lease Agreements [Member] | Minimum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Finite-lived intangible asset, useful life					1 year
Lease Agreements [Member] | Maximum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Finite-lived intangible asset, useful life					20 years
100 First LLC & 303 Second LLC [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling interest in consolidated subsidiary					$ 186,400,000	$ 175,400,000
Kilroy Realty L.P. [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of VIEs | VIE						3
Net cash provided by (used in) investing activities					(808,915,000)	$ (359,102,000)	(579,420,000)
Acquisition-related expenses					0	0	1,902,000
Original issuance costs of redeemed preferred units					0	7,589,000	0
Secured debt [Member] | Kilroy Realty L.P. [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Initial premium on outstanding amount of secured debt					800,000
Unsecured debt [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Unamortized discount (premium), net					$ 6,600,000	6,300,000
Series G Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Preferred stock dividend rate (percentage)		6.875%		6.875%
Series H Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Preferred stock dividend rate (percentage)	6.375%		6.375%
Washington [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of buildings | property					8
Number of development projects | project					1
Customer concentration risk [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of tenants | tenant					15
Concentration risk, percentage					45.70%
Customer concentration risk, largest tenant [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Concentration risk, percentage					5.90%
100 First LLC and 303 Second LLC [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling interest in consolidated subsidiary						175,400,000
Kilroy Realty Finance, Inc. [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Percentage of general partnership interest owned by wholly-owned subsidiary of the Company					1.00%
Parking Revenue [Member] | Fixed-price Contract [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Revenues					$ 26,700,000	$ 26,700,000	$ 23,300,000
Scenario, forecast [Member] | Minimum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Operating lease, right-of-use asset								$ 80,000,000
Operating lease, liability								80,000,000
Scenario, forecast [Member] | Maximum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Operating lease, right-of-use asset								95,000,000
Operating lease, liability								$ 95,000,000

Acquisitions - Operating Proper

Acquisitions - Operating Property Acquisitions (Details) $ in Millions	Dec. 21, 2018USD ($)ft²building	Jan. 31, 2018USD ($)ft²	Dec. 31, 2018USD ($)ft²building	Dec. 31, 2017property
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Number of operating properties acquired | property				0
Rentable Square Feet (unaudited) | ft²			13,232,580
Revenue contributed from acquired properties			$ 8
Net income contributed from acquired properties			$ 1.7
345, 347 & 349 Oyster Point Boulevard, South San Francisco, CA [Member]
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Rentable Square Feet (unaudited) | ft²		145,530
Occupancy percent		78.50%
Purchase price		$ 111
345 Brannan St., San Francisco, CA [Member]
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Number of buildings | building	1
Rentable Square Feet (unaudited) | ft²	110,030
Occupancy percent	99.70%
Purchase price	$ 146
345, 347 & 349 Oyster Point Boulevard, South San Francisco, CA and 345 Brannan Street, San Francisco, CA [Member]
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Number of buildings | building			4
Rentable Square Feet (unaudited) | ft²			255,560
Purchase price			$ 257

Acquisitions - Estimated Fair V

Acquisitions - Estimated Fair Values of Assets and Liabilities Assumed (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)numberofaquisitiontransactions
Assets
Land and improvements	$ 80,269
Buildings and improvements	172,059
Deferred leasing costs and acquisition-related intangible assets	13,593
Total assets acquired	265,921
Liabilities
Acquisition-related intangible liabilities	8,921
Total liabilities assumed	8,921
Net assets and liabilities acquired	$ 257,000
Number of acquisitions | numberofaquisitiontransactions	2
Below-market leases acquired	$ 8,900
Weighted average amortization period of below-market leases	9 years 10 months
In-place leases [Member]
Assets
Deferred leasing costs and acquisition-related intangible assets	$ 11,800
Liabilities
Weighted average amortization period of above-market leases in years	1 year 4 months
Deferred leasing costs [Member]
Assets
Deferred leasing costs and acquisition-related intangible assets	$ 1,800
Liabilities
Weighted average amortization period of above-market leases in years	6 years 7 months

Acquisitions - Development Proj

Acquisitions - Development Project Acquisitions and Acquisition Costs (Details) $ in Thousands	Jun. 01, 2018USD ($)abuilding	Oct. 10, 2017USD ($)a	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Asset acquisition, accrued liabilities			$ 8,921
Acquisition-related accrued liabilities			8,921
Acquisition costs, capitalized			3,800	$ 4,600	$ 500
Acquisition-related expenses			$ 0	$ 0	$ 1,902
Kilroy Oyster Point [Member]
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Area of land | a	39
Number of buildings | building	3
Purchase price	$ 308,200
Asset acquisition, accrued liabilities	$ 40,600
Little Italy, Sand Diego, California [Member]
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Area of land | a		1.2
Purchase price		$ 19,400
Acquisition-related accrued liabilities		$ 1,400

Dispositions - Operating Proper

Dispositions - Operating Property Dispositions (Details) $ in Thousands	1 Months Ended						12 Months Ended
	Dec. 31, 2018USD ($)ft²property	Nov. 30, 2018USD ($)ft²property	Sep. 30, 2017USD ($)ft²aproperty	Jan. 31, 2017USD ($)ft²property	Jul. 31, 2016USD ($)ft²aproperty	Jan. 31, 2016USD ($)ft²property	Dec. 31, 2018USD ($)ft²property	Dec. 31, 2017USD ($)ft²property	Dec. 31, 2016USD ($)ft²property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rentable square feet | ft²	13,232,580						13,232,580
Net gain (loss) on sales of land							$ 11,825	$ 449	$ (295)
Gains on sales of operating properties							$ 142,926	$ 39,507	$ 164,302
Disposal group, disposed of by sale [Member] | 1310-1327 Chesapeake Terrace, Sunnyvale, CA , Plaza Yarrow Bay Properties, and 23925, 23975, & 24025 Park Sorrento, Calabasas, CA [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | property	11						11
Rentable square feet | ft²	772,246						772,246
Proceeds from sale of property held-for-sale							$ 373,000
Disposal group, disposed of by sale [Member] | 1325-1327 Chesapeake Terrace, Sunnyvale, CA [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | property		4
Rentable square feet | ft²		266,982
Proceeds from sale of property held-for-sale		$ 160,300
Disposal group, disposed of by sale [Member] | Plaza Yarrow Bay Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | property		4
Rentable square feet | ft²		279,924
Proceeds from sale of property held-for-sale		$ 134,500
Net gain (loss) on sales of land							$ 11,800
Disposal group, disposed of by sale [Member] | 23925, 23975, & 24025 Park Sorrento, Calabasas, CA [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | property	3						3
Rentable square feet | ft²	225,340						225,340
Proceeds from sale of property held-for-sale	$ 78,200
Disposal group, disposed of by sale [Member] | 5717 Pacific Center Boulevard, San Diego, CA and Sorrento Mesa and Mission Valley Portfolio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | property								11
Rentable square feet | ft²								743,138
Proceeds from sale of property held-for-sale								$ 186,600
Disposal group, disposed of by sale [Member] | 5717 Pacific Center Boulevard, San Diego, CA [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | property				1
Rentable square feet | ft²				67,995
Proceeds from sale of property held-for-sale				$ 12,100
Disposal group, disposed of by sale [Member] | Sorrento Mesa and Mission Valley Portfolio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | property			10
Rentable square feet | ft²			675,143
Proceeds from sale of property held-for-sale			$ 174,500
Area of land | a			5
Net gain (loss) on sales of land								$ 400
Disposal group, disposed of by sale [Member] | Torrey Santa Fe Properties & 4930, 4939 & 4955 Directors Place, San Diego, CA [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | property									6
Rentable square feet | ft²									602,720
Proceeds from sale of property held-for-sale									$ 311,300
Disposal group, disposed of by sale [Member] | Torrey Santa Fe Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | property						4
Rentable square feet | ft²						465,812
Proceeds from sale of property held-for-sale						$ 262,300
Disposal group, disposed of by sale [Member] | 4930, 4939 & 4955 Directors Place, San Diego, CA [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | property					2
Rentable square feet | ft²					136,908
Proceeds from sale of property held-for-sale					$ 49,000
Area of land | a					7

Dispositions - Land Disposition

Dispositions - Land Dispositions (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Jun. 30, 2016USD ($)a	Jan. 31, 2016USD ($)a	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)a
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net gain (loss) on sales of land			$ 11,825	$ 449	$ (295)
Secured debt assumed by buyers in connection with land disposition			0	$ 0	$ 2,322
Disposal group, disposed of by sale [Member] | Plaza Yarrow Bay Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net gain (loss) on sales of land			$ 11,800
Disposal group, disposed of by sale [Member] | Carlsbad Oaks - Lot 7 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Site Acreage (unaudited) | a		7.6
Sales Price		$ 4,500
Disposal group, disposed of by sale [Member] | Carlsbad Oaks - Lots 4 & 5 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Site Acreage (unaudited) | a	11.2
Sales Price	$ 6,000
Disposal group, disposed of by sale [Member] | Carlsbad Oaks - Lot 8 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Site Acreage (unaudited) | a	13.2
Sales Price	$ 8,900
Disposal group, disposed of by sale [Member] | Carlsbad Oaks - Lots 7, 4 & 5, 8 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Site Acreage (unaudited) | a					32
Sales Price					$ 19,400
Secured debt assumed by buyers in connection with land disposition					$ 2,300

Dispositions - Restricted Cash

Dispositions - Restricted Cash Related to Dispositions (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Disposal group, disposed of by sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Restricted cash	$ 113,100,000	$ 0

Deferred Leasing Costs and Ac_3

Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, net - Deferred Leasing Costs and Acquisition-Related Intangible Assets and Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, Net
Total deferred leasing costs and acquisition-related intangible assets, net	$ 197,574	$ 183,728
Acquisition-related Intangible Liabilities, Net [Abstract]
Total acquisitions-related intangible liabilities, net	29,138	30,639
Deferred leasing costs [Member]
Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, Net
Finite-lived intangible assets/liabilities, gross	266,905	248,598
Accumulated amortization	(100,805)	(101,917)
Finite-lived intangible assets	166,100	146,681
Above market leases [Member]
Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, Net
Finite-lived intangible assets/liabilities, gross	2,836	4,199
Accumulated amortization	(2,150)	(3,068)
Finite-lived intangible assets	686	1,131
In-place leases [Member]
Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, Net
Finite-lived intangible assets/liabilities, gross	66,526	82,097
Accumulated amortization	(36,174)	(46,625)
Finite-lived intangible assets	30,352	35,472
Below-Market Ground Lease Obligation [Member]
Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, Net
Finite-lived intangible assets/liabilities, gross	490	490
Accumulated amortization	(54)	(46)
Finite-lived intangible assets	436	444
Below Market Operating Lease [Member]
Acquisition-related Intangible Liabilities, Net [Abstract]
Acquisition-related intangible liabilities, gross	53,523	65,440
Accumulated amortization	(29,978)	(40,495)
Acquisition-related intangible liabilities, net	23,545	24,945
Above-Market Ground Lease Obligation [Member]
Acquisition-related Intangible Liabilities, Net [Abstract]
Acquisition-related intangible liabilities, gross	6,320	6,320
Accumulated amortization	(727)	(626)
Acquisition-related intangible liabilities, net	$ 5,593	$ 5,694

Deferred Leasing Costs and Ac_4

Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, net - Amortization of Deferred Leasing Costs and Acquisition-Related Intangibles (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to deferred leasing costs and acquisition-related intangibles	$ 40,415	$ 41,704	$ 33,057
Deferred leasing costs [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to deferred leasing costs and acquisition-related intangibles	34,341	31,675	28,639
Estimated annual amortization related to acquisition-related intangible assets
Finite-lived intangible assets, 2019	31,980
Finite-lived intangible assets, 2020	26,868
Finite-lived intangible assets, 2021	21,787
Finite-lived intangible assets, 2022	18,683
Finite-lived intangible assets, 2023	14,914
Finite-lived intangible assets, thereafter	51,868
Finite-lived intangible assets	166,100	146,681
Above market leases [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to deferred leasing costs and acquisition-related intangibles	444	2,240	1,509
Estimated annual amortization related to acquisition-related intangible assets
Finite-lived intangible assets, 2019	192
Finite-lived intangible assets, 2020	38
Finite-lived intangible assets, 2021	38
Finite-lived intangible assets, 2022	38
Finite-lived intangible assets, 2023	38
Finite-lived intangible assets, thereafter	342
Finite-lived intangible assets	686	1,131
In-place leases [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to deferred leasing costs and acquisition-related intangibles	15,915	18,650	11,676
Estimated annual amortization related to acquisition-related intangible assets
Finite-lived intangible assets, 2019	16,675
Finite-lived intangible assets, 2020	5,963
Finite-lived intangible assets, 2021	2,861
Finite-lived intangible assets, 2022	1,589
Finite-lived intangible assets, 2023	648
Finite-lived intangible assets, thereafter	2,616
Finite-lived intangible assets	30,352	35,472
Below-Market Ground Lease Obligation [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to deferred leasing costs and acquisition-related intangibles	8	8	8
Estimated annual amortization related to acquisition-related intangible assets
Finite-lived intangible assets, 2019	8
Finite-lived intangible assets, 2020	8
Finite-lived intangible assets, 2021	8
Finite-lived intangible assets, 2022	8
Finite-lived intangible assets, 2023	8
Finite-lived intangible assets, thereafter	396
Finite-lived intangible assets	436	444
Below Market Operating Lease [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization Of Intangible Liabilities	(10,192)	(10,768)	(8,674)
Estimated annual amortization related to acquisition-related intangible liabilities
Acquisition-related intangible liabilities, 2019	(7,779)
Acquisition-related intangible liabilities, 2020	(4,621)
Acquisition-related intangible liabilities, 2021	(1,938)
Acquisition-related intangible liabilities, 2022	(1,486)
Acquisition-related intangible liabilities, 2023	(988)
Acquisition-related intangible liabilities, thereafter	(6,733)
Acquisition-related intangible liabilities	(23,545)	(24,945)
Above-Market Ground Lease Obligation [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization Of Intangible Liabilities	(101)	(101)	$ (101)
Estimated annual amortization related to acquisition-related intangible liabilities
Acquisition-related intangible liabilities, 2019	(100)
Acquisition-related intangible liabilities, 2020	(100)
Acquisition-related intangible liabilities, 2021	(100)
Acquisition-related intangible liabilities, 2022	(100)
Acquisition-related intangible liabilities, 2023	(100)
Acquisition-related intangible liabilities, thereafter	(5,093)
Acquisition-related intangible liabilities	$ (5,593)	$ (5,694)

Receivables - Current Receivabl

Receivables - Current Receivables and Deferred Rent Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current Receivables, net
Current receivables	$ 24,815	$ 19,235
Allowance for uncollectible tenant receivables	(4,639)	(2,309)
Current receivables, net	20,176	16,926
Deferred Rent Receivables, net
Deferred rent receivables	270,346	249,629
Allowance for deferred rent receivables	(3,339)	(3,238)
Deferred rent receivables, net	$ 267,007	$ 246,391

Prepaid Expenses and Other As_3

Prepaid Expenses and Other Assets, Net - Schedule of Prepaid Expenses and Other Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Furniture, fixtures and other long-lived assets, net	$ 36,833	$ 39,686
Notes receivable	2,113	19,912
Prepaid expenses & acquisition deposits	13,927	55,108
Total Prepaid Expenses and Other Assets, Net	52,873	114,706
Proceeds received from repayment of note receivable	15,100	$ 0	$ 0
Notes receivable, valuation allowance	$ 2,900

Secured and Unsecured Debt of_4

Secured and Unsecured Debt of the Company - Narrative (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Secured debt	$ 335,531,000	$ 340,800,000
Line of credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	150,000,000
Unsecured debt [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,600,000,000	$ 2,000,000,000

Secured and Unsecured Debt of_5

Secured and Unsecured Debt of the Operating Partnership - Secured Debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Secured Debt
Secured debt	$ 335,531	$ 340,800
Debt premium	800
Kilroy Realty L.P. [Member]
Secured Debt
Long-term debt, gross	2,955,811
Secured debt	335,531	340,800
Unamortized Deferred Financing Costs	(17,400)
Kilroy Realty L.P. [Member] | Secured debt [Member]
Secured Debt
Secured debt	336,570	341,975
Unamortized Deferred Financing Costs	(1,039)	(1,175)
Long-term debt	335,531	340,800
Debt premium	800
Net book value of properties pledged as collateral for secured debt	$ 324,600
Kilroy Realty L.P. [Member] | Secured debt [Member] | 3.57% Mortgage Payable due December 2026 [Member]
Secured Debt
Stated interest rate	3.57%
Effective interest rate	3.57%
Maturity date	Dec. 1, 2026
Long-term debt, gross	$ 170,000	170,000
Kilroy Realty L.P. [Member] | Secured debt [Member] | 4.48% Mortgage Payable due July 2027 [Member]
Secured Debt
Stated interest rate	4.48%
Effective interest rate	4.48%
Maturity date	Jul. 1, 2027
Long-term debt, gross	$ 91,332	93,081
Kilroy Realty L.P. [Member] | Secured debt [Member] | 6.05% Mortgage Payable Due June 1, 2019 [Member]
Secured Debt
Stated interest rate	6.05%
Effective interest rate	3.50%
Maturity date	Jun. 1, 2019
Long-term debt, gross	$ 75,238	78,894
Debt premium	$ 800	$ 2,600

Secured and Unsecured Debt of_6

Secured and Unsecured Debt of the Operating Partnership - Unsecured Senior Notes Table (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Unsecured debt, net	$ 2,552,070,000	$ 2,006,263,000
Unsecured debt [Member]
Debt Instrument [Line Items]
Unamortized discount (premium), net	6,600,000	6,300,000
Unamortized debt issuance expense	15,400,000	12,500,000
Kilroy Realty L.P. [Member]
Debt Instrument [Line Items]
Unamortized debt issuance expense	17,400,000
Long-term debt, gross	2,955,811,000
Unsecured debt, net	2,552,070,000	2,006,263,000
Kilroy Realty L.P. [Member] | Secured debt [Member]
Debt Instrument [Line Items]
Unamortized debt issuance expense	1,039,000	1,175,000
Kilroy Realty L.P. [Member] | Unsecured debt [Member]
Debt Instrument [Line Items]
Unsecured debt, net	$ 2,402,979,000	2,006,263,000
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 4.750% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Maturity date	Dec. 15, 2028
Stated interest rate	4.75%
Effective interest rate	4.80%
Long-term debt, gross	$ 400,000,000	0
Unamortized discount and deferred financing costs	(4,960,000)	0
Unsecured debt, net	$ 395,040,000	0
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 4.350% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Maturity date	Oct. 18, 2026
Stated interest rate	4.35%
Effective interest rate	4.35%
Long-term debt, gross	$ 200,000,000	0
Unamortized discount and deferred financing costs	(1,375,000)	0
Unsecured debt, net	$ 198,625,000	0
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 4.300% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Maturity date	Jul. 18, 2026
Stated interest rate	4.30%
Effective interest rate	4.30%
Long-term debt, gross	$ 50,000,000	0
Unamortized discount and deferred financing costs	(342,000)	0
Unsecured debt, net	$ 49,658,000	0
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 3.450% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Maturity date	Dec. 15, 2024
Stated interest rate	3.45%
Effective interest rate	3.47%
Long-term debt, gross	$ 425,000,000	425,000,000
Unamortized discount and deferred financing costs	(3,493,000)	(4,047,000)
Unsecured debt, net	$ 421,507,000	420,953,000
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 3.450% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Maturity date	Feb. 17, 2029
Stated interest rate	3.45%
Effective interest rate	3.45%
Long-term debt, gross	$ 75,000,000	75,000,000
Unamortized discount and deferred financing costs	(432,000)	(475,000)
Unsecured debt, net	$ 74,568,000	74,525,000
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 3.350% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Maturity date	Feb. 17, 2027
Stated interest rate	3.35%
Effective interest rate	3.35%
Long-term debt, gross	$ 175,000,000	175,000,000
Unamortized discount and deferred financing costs	(941,000)	(1,056,000)
Unsecured debt, net	$ 174,059,000	173,944,000
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 4.375% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Maturity date	Oct. 1, 2025
Stated interest rate	4.375%
Effective interest rate	4.444%
Long-term debt, gross	$ 400,000,000	400,000,000
Unamortized discount and deferred financing costs	(3,738,000)	(4,292,000)
Unsecured debt, net	$ 396,262,000	395,708,000
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 4.250% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Maturity date	Aug. 15, 2029
Stated interest rate	4.25%
Effective interest rate	4.35%
Long-term debt, gross	$ 400,000,000	400,000,000
Unamortized discount and deferred financing costs	(5,632,000)	(6,164,000)
Unsecured debt, net	$ 394,368,000	393,836,000
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 3.800% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Maturity date	Jan. 15, 2023
Stated interest rate	3.80%
Effective interest rate	3.80%
Long-term debt, gross	$ 300,000,000	300,000,000
Unamortized discount and deferred financing costs	(1,108,000)	(1,382,000)
Unsecured debt, net	$ 298,892,000	298,618,000
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 6.625% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Maturity date	Jun. 1, 2020
Stated interest rate	6.625%
Effective interest rate	6.744%
Long-term debt, gross	$ 0	250,000,000
Unamortized discount and deferred financing costs	0	(1,321,000)
Unsecured debt, net	$ 0	$ 248,679,000

Secured and Unsecured Debt of_7

Secured and Unsecured Debt of the Operating Partnership - Unsecured Senior Notes - Registered Offerings and Private Placement (Details) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Loss on early extinguishment of debt		$ 12,623,000	$ 5,312,000	$ 0
Kilroy Realty L.P. [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 2,955,811,000	2,955,811,000
Loss on early extinguishment of debt		12,623,000	5,312,000	$ 0
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 4.750% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	400,000,000	400,000,000	0
Debt issuance discount	$ 1,500,000	$ 1,500,000
Maturity date		Dec. 15, 2028
Stated interest rate	4.75%	4.75%
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 6.625% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	$ 0	250,000,000
Maturity date		Jun. 1, 2020
Stated interest rate	6.625%	6.625%
Extinguishment of debt	$ 11,800,000
Write off of unamortized discount and deferred financing costs	800,000
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 3.450% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 425,000,000	$ 425,000,000	425,000,000
Maturity date		Dec. 15, 2024
Stated interest rate	3.45%	3.45%
Debt issuance cost			600,000
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 4.800% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 325,000,000
Stated interest rate			4.80%
Extinguishment of debt			$ 5,000,000
Write off of unamortized discount and deferred financing costs			300,000
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 3.350% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 175,000,000	$ 175,000,000	175,000,000
Maturity date		Feb. 17, 2027
Stated interest rate	3.35%	3.35%
Kilroy Realty L.P. [Member] | Unsecured debt [Member] | 3.450% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 75,000,000	$ 75,000,000	$ 75,000,000
Maturity date		Feb. 17, 2029
Stated interest rate	3.45%	3.45%
Kilroy Realty L.P. [Member] | Private placement [Member] | Unsecured debt [Member] | 3.35% Series A Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 175,000,000	$ 175,000,000
Kilroy Realty L.P. [Member] | Private placement [Member] | Unsecured debt [Member] | 3.45% Series B Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 75,000,000	$ 75,000,000
Kilroy Realty L.P. [Member] | Private placement [Member] | Unsecured debt [Member] | Series A and B Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Operating partnership, payment percent		5.00%
Operating partnership, total payment percentage		100.00%

Secured and Unsecured Debt of_8

Secured and Unsecured Debt of the Operating Partnership - Unsecured Revolving Credit Facility and Term Loan Facility (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017
Terms of the Credit Facility
Outstanding borrowings		$ 45,000,000	$ 0
Borrowings on unsecured debt		120,000,000	0	$ 0
Line of credit [Member]
Terms of the Credit Facility
Total borrowing capacity		150,000,000
Kilroy Realty L.P. [Member]
Terms of the Credit Facility
Outstanding borrowings		45,000,000	0
Unamortized debt issuance expense		17,400,000
Borrowings on unsecured debt		120,000,000	0	$ 0
Kilroy Realty L.P. [Member] | Revolving credit facility [Member]
Terms of the Credit Facility
Outstanding borrowings		45,000,000	0
Remaining borrowing capacity		705,000,000	750,000,000
Total borrowing capacity		$ 750,000,000	$ 750,000,000		$ 600,000,000
Interest rate		3.48%	2.56%
Facility fee-annual rate		0.20%	0.20%
Maturity date		Jul. 1, 2022	Jul. 1, 2019
Contingent additional borrowings		$ 600,000,000
Unamortized debt issuance expense		4,700,000	$ 6,000,000
Kilroy Realty L.P. [Member] | Line of credit [Member]
Terms of the Credit Facility
Total borrowing capacity		150,000,000	150,000,000
Kilroy Realty L.P. [Member] | $150.0 million term loan facility [Member] | Line of credit [Member]
Terms of the Credit Facility
Outstanding borrowings	$ 150,000,000	150,000,000	0
Remaining borrowing capacity		$ 0	$ 150,000,000
Interest rate		3.49%	2.66%
Undrawn facility fee-annual rate		0.20%	0.20%
Maturity date		Jul. 1, 2022	Jul. 1, 2022
Unamortized debt issuance expense		$ 900,000	$ 1,200,000
Line of credit facility, increase (decrease)	30,000,000
Borrowings on unsecured debt	$ 120,000,000
Kilroy Realty L.P. [Member] | London Interbank Offered Rate (LIBOR) [Member] | Revolving credit facility [Member]
Terms of the Credit Facility
Basis spread on LIBOR		1.00%	1.00%
Kilroy Realty L.P. [Member] | London Interbank Offered Rate (LIBOR) [Member] | $150.0 million term loan facility [Member] | Line of credit [Member]
Terms of the Credit Facility
Basis spread on LIBOR		1.10%	1.10%

Secured and Unsecured Debt of_9

Secured and Unsecured Debt of the Operating Partnership - Debt Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Stated debt maturities and scheduled amortization payments, excluding debt discounts
Debt premium	$ 800
Kilroy Realty L.P. [Member]
Stated debt maturities and scheduled amortization payments, excluding debt discounts
2,019	76,309
2,020	5,137
2,021	5,342
2,022	200,554
2,023	305,775
Thereafter	2,362,694
Total aggregate principal value	2,955,811
Unamortized debt issuance expense	(17,400)
Kilroy Realty L.P. [Member] | Unsecured senior notes [Member]
Stated debt maturities and scheduled amortization payments, excluding debt discounts
Debt issuance discount	6,600
Kilroy Realty L.P. [Member] | Secured debt [Member]
Stated debt maturities and scheduled amortization payments, excluding debt discounts
Unamortized debt issuance expense	(1,039)	$ (1,175)
Debt premium	$ 800

Secured and Unsecured Debt o_10

Secured and Unsecured Debt of the Operating Partnership - Capitalized Interest and Loan Fees (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Interest expense	$ 49,721	$ 66,040	$ 55,803
Kilroy Realty L.P. [Member]
Debt Instrument [Line Items]
Gross interest expense	117,789	112,577	105,263
Capitalized interest and deferred financing costs	(68,068)	(46,537)	(49,460)
Interest expense	$ 49,721	$ 66,040	$ 55,803

Deferred Revenue and Acquisit_3

Deferred Revenue and Acquisition Related Liabilities, net - Deferred Revenue and Acquisition-Related Intangible Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Revenue Arrangement [Line Items]
Acquisition-related intangible liabilities, net	$ 29,138	$ 30,639
Deferred revenue and acquisition-related intangible liabilities, net	149,646	145,890
Tenant funded tenant improvements [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue	104,558	104,260
Other deferred revenue [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue	$ 15,950	$ 10,991

Deferred Revenue and Acquisit_4

Deferred Revenue and Acquisition Related Liabilities, net - Estimated Amortization of Deferred Revenue (Details) - Tenant funded tenant improvements [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Deferred revenues amortized and recognized as rental income	$ 18,400	$ 16,800	$ 13,200
Deferred Revenue, Future Amortization Recognized By Year [Abstract]
2,019	16,973
2,020	16,265
2,021	14,612
2,022	13,603
2,023	11,857
Thereafter	31,248
Total	$ 104,558

Noncontrolling Interests on t_3

Noncontrolling Interests on the Company's Consolidated Financial Statements - Narrative (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)d$ / sharesshares	Dec. 31, 2017USD ($)shares	Nov. 30, 2017USD ($)	Nov. 30, 2016USD ($)	Aug. 30, 2016USD ($)ft²
Noncontrolling Interest [Line Items]
Ownership interest of noncontrolling interest	2.00%	2.10%
Common stock, par value (in dollars per share) | $ / shares	$ 0.01
Trading days | d	10
Aggregate value upon redemption of outstanding noncontrolling common units	$ 126,400	$ 154,500
Noncontrolling interest in consolidated subsidiary	192,363	181,575
100 First LLC & 303 Second LLC [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest in consolidated subsidiary	$ 186,400	175,400
Redwood LLC [Member]
Noncontrolling Interest [Line Items]
Percentage of general partnership interest owned by the company in the Operating Partnership	93.00%
Noncontrolling interest in consolidated subsidiary	$ 6,000	$ 6,200
Capital units [Member] | Kilroy Realty L.P. [Member]
Noncontrolling Interest [Line Items]
Noncontrolling common units (in units) | shares	2,025,287	2,077,193
Exchange of common units of the Operating Partnership (in units) | shares	51,906
Consolidated property partnerships [Member] | Norges Bank Real Estate Management (NBREM) [Member]
Noncontrolling Interest [Line Items]
Percentage of general partnership interest owned by the company in the Operating Partnership					44.00%
Ownership interest of noncontrolling interest					44.00%
Real estate investments, joint ventures					$ 1,200,000
Other ownership interests, contributed capital			$ 54,400		452,900
Other ownership interests, mortgage debt					55,300
Consolidated property partnerships, tranche one [Member] | Norges Bank Real Estate Management (NBREM) [Member]
Noncontrolling Interest [Line Items]
Other ownership interests, contributed capital					191,400
Other ownership interests, contributed capital, working capital contribution					$ 2,100
Consolidated property partnerships, tranche one [Member] | 100 First LLC [Member]
Noncontrolling Interest [Line Items]
Area of real estate property | ft²					467,095
Consolidated property partnerships, tranche two [Member] | Norges Bank Real Estate Management (NBREM) [Member]
Noncontrolling Interest [Line Items]
Other ownership interests, contributed capital				$ 261,500
Other ownership interests, mortgage debt					$ 55,300
Other ownership interests, contributed capital, working capital contribution				$ 2,900
Consolidated property partnerships, tranche two [Member] | 303 Second Street [Member]
Noncontrolling Interest [Line Items]
Area of real estate property | ft²					740,047
Operating Partnership [Member]
Noncontrolling Interest [Line Items]
Percentage of general partnership interest owned by the company in the Operating Partnership	98.00%	97.90%

Noncontrolling Interests on t_4

Noncontrolling Interests on the Operating Partnership's Consolidated Financial Statements - Narrative (Details) - Consolidated property partnerships [Member] - Norges Bank Real Estate Management (NBREM) [Member] $ in Millions	Nov. 30, 2017USD ($)	Aug. 30, 2016USD ($)property
Noncontrolling Interest [Line Items]
Number of buildings | property		2
Real estate investments, joint ventures		$ 1,200
Other ownership interests, contributed capital	$ 54.4	$ 452.9
Company owned general partnership interest		44.00%
Other ownership interests, mortgage debt		$ 55.3

Stockholders' Equity of the C_3

Stockholders' Equity of the Company - Narrative (Details) - USD ($)	Aug. 08, 2018	Jan. 31, 2017	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 01, 2019	Aug. 15, 2017	Mar. 30, 2017	Feb. 23, 2016
Class of Stock [Line Items]
Original issuance costs of redeemed preferred units				$ 0	$ 7,589,000	$ 0
Common stock, value, issued				1,007,000	986,000
Common stock, shares issued (in shares)		4,427,500
Aggregate net proceeds after selling commissions		$ 308,800,000		$ 130,693,000	326,058,000	31,117,000
Shares issued, price per share (in dollars per share)		$ 1.90
Stock repurchase program, number of shares authorized to be repurchased										4,000,000
Stock repurchase program, remaining number of shares authorized to be repurchased				4,935,826						4,988,025
Stock repurchased during period, shares			52,199
Treasury stock acquired, average cost per share			$ 55.45
Stock repurchased during period, value			$ 2,900,000
Issuance of Equity under ATM Program [Member]
Class of Stock [Line Items]
Aggregate net proceeds after selling commissions				$ 132,100,000	$ 17,500,000	$ 31,900,000
Shares issued, price per share (in dollars per share)				$ 73.64	$ 75.40	$ 71.50
Aggregate gross proceeds				$ 133,800,000	$ 17,700,000	$ 32,300,000
2014 At-The-Market Program [Member]
Class of Stock [Line Items]
Aggregate gross proceeds				300,000,000
2018 At-The-Market Program [Member]
Class of Stock [Line Items]
Aggregate gross proceeds				$ 500,000,000
Series H Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock (in shares)								4,000,000
Preferred stock, liquidation preference per share (in dollars per share)								$ 25
Preferred stock liquidation preference								$ 100,000,000
Series G Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock (in shares)									4,000,000
Preferred stock, liquidation preference per share (in dollars per share)									$ 25
Preferred stock liquidation preference									$ 100,000,000
Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares issued (in shares)				100,746,988	98,620,333
Common Stock [Member] | 2014 At-The-Market Program [Member]
Class of Stock [Line Items]
Common stock, shares issued (in shares)				1,369,729
Common Stock [Member] | 2018 At-The-Market Program [Member]
Class of Stock [Line Items]
Common stock, shares issued (in shares)				447,466
At market stock offering program remained available for issuance				$ 466,200,000
Forward Equity Offering [Member]
Class of Stock [Line Items]
Common stock, value, issued	$ 360,500,000
Stock issued, price per share (in dollar per share)	$ 72.10
Forward Equity Offering [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock issued (in shares)	5,000,000
Scenario, forecast [Member] | Forward Equity Offering [Member]
Class of Stock [Line Items]
Stock issued, price per share (in dollar per share)							$ 71.68

Stockholders' Equity of the C_4

Stockholders' Equity of the Company - At-The-Market Offering and Derivatives and Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Dividends Payable [Line Items]
Weighted average price per share of common stock (in dollars per share)	$ 1.90
Aggregate net proceeds after selling commissions	$ 308,800	$ 130,693	$ 326,058	$ 31,117
Accrued dividend and distributions
Accrued dividends and distributions		47,559	43,448
Common stockholders and noncontrolling unitholders [Member]
Accrued dividend and distributions
Accrued dividends and distributions		47,559	43,448
Common Stock [Member]
Accrued dividend and distributions
Accrued dividends and distributions		$ 45,840	$ 41,914
Summary of shares and units
Common stock		100,746,988	98,620,333
Capital units [Member]
Accrued dividend and distributions
Accrued dividends and distributions		$ 922	$ 883
Restricted Stock Units (RSUs) [Member]
Summary of shares and units
RSUs		1,711,628	1,488,724
Issuance of Equity under ATM Program [Member]
Dividends Payable [Line Items]
Shares of common stock sold during the period (in shares)		1,817,195	235,077	451,398
Weighted average price per share of common stock (in dollars per share)		$ 73.64	$ 75.40	$ 71.50
Aggregate gross proceeds		$ 133,800	$ 17,700	$ 32,300
Aggregate net proceeds after selling commissions		132,100	17,500	31,900
Kilroy Realty L.P. [Member]
Dividends Payable [Line Items]
Aggregate net proceeds after selling commissions		130,693	326,058	$ 31,117
Accrued dividend and distributions
Accrued dividends and distributions		$ 47,559	$ 43,448
Kilroy Realty L.P. [Member] | Capital units [Member]
Summary of shares and units
Noncontrolling common units (in units)		2,025,287	2,077,193
Kilroy Realty L.P. [Member] | Restricted Stock Units (RSUs) [Member]
Accrued dividend and distributions
Accrued dividends and distributions		$ 797	$ 651
Kilroy Realty L.P. [Member] | Market measure-based Restricted Stock Units (RSUs) [Member]
Summary of shares and units
Number of RSUs outstanding (in shares)		1,018,337	665,110

Partners' Capital of the Oper_2

Partners' Capital of the Operating Partnership - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Aug. 15, 2017	Mar. 30, 2017	Jan. 31, 2017	Aug. 31, 2012	Mar. 31, 2012	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Class of Stock [Line Items]
Original issuance costs of redeemed preferred units						$ 0	$ 7,589	$ 0
Common stock, shares issued (in shares)			4,427,500
Aggregate net proceeds after selling commissions			$ 308,800			$ 130,693	$ 326,058	$ 31,117
Common stock, par value (in dollars per share)						$ 0.01
Brannan St Project [Member]
Class of Stock [Line Items]
Business acquisition, equity interest issued or issuable (in shares)							867,701
Share price (in dollars per share)									$ 55.36
Common stock, par value (in dollars per share)									$ 0.01
Series H Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock (in shares)	4,000,000
Preferred stock, dividend rate	6.375%			6.375%
Series G Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock (in shares)		4,000,000
Preferred stock, dividend rate		6.875%			6.875%

Partners' Capital of the Oper_3

Partners' Capital of the Operating Partnership - At-The-Market Stock Offering, Common Units and Accrued Distributions (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Aggregate net proceeds after selling commissions	$ 308,800	$ 130,693	$ 326,058	$ 31,117
Summary of units
Ownership interest of noncontrolling interest		2.00%	2.10%
Accrued distributions
Accrued dividends and distributions		$ 47,559	$ 43,448
Common Stock [Member]
Accrued distributions
Accrued dividends and distributions		45,840	41,914
Capital units [Member]
Accrued distributions
Accrued dividends and distributions		$ 922	$ 883
Issuance of Equity under ATM Program [Member]
Class of Stock [Line Items]
Shares of common stock contributed by the Company (in shares)		1,817,195	235,077	451,398
Common units exchanged for shares of common stock by the Company (in units)		1,817,195	235,077	451,398
Aggregate gross proceeds		$ 133,800	$ 17,700	$ 32,300
Aggregate net proceeds after selling commissions		132,100	17,500	31,900
Kilroy Realty L.P. [Member]
Class of Stock [Line Items]
Aggregate net proceeds after selling commissions		130,693	326,058	$ 31,117
Accrued distributions
Accrued dividends and distributions		$ 47,559	$ 43,448
Kilroy Realty L.P. [Member] | Restricted Stock Units (RSUs) [Member]
Summary of units
RSUs (in shares)		1,711,628	1,488,724
Accrued distributions
Accrued dividends and distributions		$ 797	$ 651
Kilroy Realty L.P. [Member] | Market measure-based Restricted Stock Units (RSUs) [Member]
Summary of units
Number of RSUs outstanding (in shares)		1,018,337	665,110
Kilroy Realty L.P. [Member] | Partners Capital Common Unit [Member]
Accrued distributions
Accrued dividends and distributions		$ 47,559	$ 43,448
Kilroy Realty L.P. [Member] | Partners capital general partner [Member]
Accrued distributions
Accrued dividends and distributions		45,840	41,914
Kilroy Realty L.P. [Member] | Partners capital limited partner [Member]
Accrued distributions
Accrued dividends and distributions		$ 922	$ 883
Kilroy Realty L.P. [Member] | Capital units [Member]
Summary of units
Company owned common units in the Operating Partnership (in units)		100,746,988	98,620,333
Noncontrolling common units of the Operating Partnership (in units)		2,025,287	2,077,193
Operating Partnership [Member]
Summary of units
Company owned general partnership interest		98.00%	97.90%

Share-Based Compensation - Stoc

Share-Based Compensation - Stockholder Approved Share-Based Incentive Compensation Plan (Details)	Dec. 31, 2018shares
Kilroy Realty 2006 Incentive Award Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares available for grant	600,000
Shareholder Meeting Date May 21, 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares requested	9,220,000

Share-Based Compensation - 2018

Share-Based Compensation - 2018, 2017 and 2016 Share-Based Compensation Grants (Details) - shares	Dec. 27, 2018	Feb. 24, 2017	Jan. 28, 2016	Feb. 28, 2017	Feb. 28, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Stock Units (RSUs) [Member] | Executive officer share-based compensation programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)	161,290		294,821	229,976	282,038
Restricted Stock Units (RSUs) [Member] | Chief Executive Officer [Member] | Executive officer share-based compensation programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)	483,871
Market measure-based Restricted Stock Units (RSUs) [Member] | Executive officer share-based compensation programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)	80,647	130,956	168,077		158,205
Market measure-based Restricted Stock Units (RSUs) [Member] | Chief Executive Officer [Member] | Executive officer share-based compensation programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)	266,130
Time-Based Restricted Stock Units (RSUs) [Member] | Executive officer share-based compensation programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)	80,643		126,744	99,020	123,833	14,999	43,081	47,003
Time-Based Restricted Stock Units (RSUs) [Member] | Chief Executive Officer [Member] | Executive officer share-based compensation programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)	217,741
December 2018 Market-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)						346,777
Time-Based Restricted Stock Units (RSUs), 2018 Special Time-Based RSU Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)						298,384

Share-Based Compensation - 20_2

Share-Based Compensation - 2018 Special Market-Based RSU Grant (Details) - December 2018 Market-Based RSUs [Member] - USD ($) $ / shares in Units, $ in Millions	Dec. 27, 2018	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)		346,777
Award vesting period		3 years
Vesting criteria, one		75.00%
Vesting criteria, two		25.00%
Fair value RSUs granted	$ 23.8
Fair value per share on valuation date (in dollars per share)	$ 68.66	$ 68.66
Expected share price volatility (in dollars per share)	23.00%
Risk-free interest rate	2.40%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target percent		0.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target percent		200.00%

Share-Based Compensation - 20_3

Share-Based Compensation - 2018, 2017 and 2016 Annual Performance-Based RSU Grants (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 27, 2018	Feb. 14, 2018	Feb. 24, 2017	Jan. 28, 2016	Feb. 28, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
2018 Performance-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period						3 years
Vesting criteria, one						100.00%
Vesting criteria, two						50.00%
Vesting criteria, three						50.00%
Performance-based RSUs achievement target, participant one, percent						175.00%
Performance-based RSUs achievement target, all ofther participants, percent						150.00%
Fair value RSUs granted		$ 10.8
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Fair value per share on valuation date (in dollars per share)		$ 70.08
Expected share price volatility (in dollars per share)		20.00%
Risk-free interest rate		2.37%
Market measure-based Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Fair value per share on valuation date (in dollars per share)						$ 68.51
2017 Performance-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period							3 years
Vesting criteria, one							100.00%
Vesting criteria, two							30.00%
Vesting criteria, three							40.00%
Performance-based RSUs achievement target, percent							131.00%
Fair value RSUs granted			$ 10.3
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Fair value per share on valuation date (in dollars per share)			$ 80.89
Expected share price volatility (in dollars per share)			21.00%
Risk-free interest rate			1.39%
2016 Performance-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period								3 years
Performance-based RSUs achievement target, percent								144.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Fair value per share on valuation date (in dollars per share)				$ 57.08
Expected share price volatility (in dollars per share)				26.00%
Risk-free interest rate				1.13%
Executive officer share-based compensation programs [Member] | Market measure-based Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)	80,647		130,956	168,077	158,205
Market measure-based RSU estimate of probable [Member] | Market measure-based Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated RSUs earned based on FFO		254,235	170,994	241,438
Chief Executive Officer [Member] | Executive officer share-based compensation programs [Member] | Market measure-based Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)	266,130
Fair value RSUs granted				$ 9.6

Share-Based Compensation Decemb

Share-Based Compensation December 2018, Annual 2018, 2017 and 2016 Time-Based RSU Grants (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 27, 2018	Feb. 14, 2018	Jan. 29, 2018	Feb. 24, 2017	Feb. 03, 2017	Jan. 28, 2016	Feb. 28, 2017	Feb. 28, 2018	Dec. 31, 2018	Dec. 31, 2017
2018 Performance-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting criteria, one									100.00%
Vesting criteria, two									50.00%
Fair value RSUs granted		$ 10.8
Time-Based Restricted Stock Units (RSUs), 2018 Special Time-Based RSU Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value RSUs granted	$ 18.5
Fair value per share (in dollars per share)	$ 62
Time-Based Restricted Stock Units (RSUs), 2018 Time-Based RSU Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value RSUs granted								$ 8.4
Fair value per share (in dollars per share)		$ 66.46						$ 70.37
RSUs granted (in units)		67,818	56,015
Time-Based Restricted Stock Units (RSUs), 2017 Time-Based RSU Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value RSUs granted							$ 7.5
Fair value per share (in dollars per share)				$ 77.16	$ 73.30
RSUs granted (in units)				57,901	41,119
Time-Based Restricted Stock Units (RSUs), 2016 Time-Based RSU Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value RSUs granted						$ 7.1
Fair value per share (in dollars per share)						$ 56.23
2017 Performance-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting criteria, one										100.00%
Vesting criteria, two										30.00%
Fair value RSUs granted				$ 10.3
December 2018 Time-Based RSUs [Member] [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting criteria, one									50.00%
Vesting criteria, two									50.00%
Chief Executive Officer [Member] | Executive officer share-based compensation programs [Member] | Market measure-based Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value RSUs granted						$ 9.6

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Market-Measure Based RSUs 1 (Details) - Market measure-based Restricted Stock Units (RSUs) [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSU weighted average fair value, beginning balance (in dollars per share)	$ 68.83
Fair value per share on valuation date (in dollars per share)	$ 68.51
Vested (in shares)	265,918	194,991	36,914
Weighted average fair value, vested (in dollars per share)	$ 74.25
Weighted average fair value, issuance of dividend equivalents (in dollars per share)	71.75
Weighted average fair value, forfeited (in dollars per share)
RSU weighted average fair value, ending balance (in dollars per share)	$ 67.29	$ 68.83
Nonvested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	601,012	170,994	258,393
Fair value per share on valuation date (in dollars per share)	$ 68.51	$ 78.97	$ 57.36
Vested (in shares)	261,875
Issuance of dividend equivalents (in shares)	14,090
Forfeited (in shares)	0
Number of RSUs outstanding, ending balance (in shares)	1,018,337
Vested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested RSUs, beginning balance	55,672
Granted (in shares)	1,067
Vested (in shares)	261,875
Settled (in shares)	(285,818)
Issuance of dividend equivalents (in shares)	2,976
Forfeited (in shares)	(11)
Vested RSUs, ending balance	35,761	55,672
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total RSUs, beginning balance (in shares)	720,782
Granted (in shares)	602,079
Vested (in shares)	0
Settled (in shares)	(285,818)
Issuance of dividend equivalents (in shares)	17,066
Forfeited (in shares)	(11)
Total RSUs, ending balance (in shares)	1,054,098	720,782
Kilroy Realty 2006 Incentive Award Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Settled (in shares)	(139,933)
Kilroy Realty L.P. [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of RSUs outstanding, beginning balance (in shares)	665,110
Number of RSUs outstanding, ending balance (in shares)	1,018,337	665,110

Share-Based Compensation - Su_2

Share-Based Compensation - Summary of Market-Measure Based RSUs 2 (Details) - Market measure-based Restricted Stock Units (RSUs) [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value per share on valuation date (in dollars per share)	$ 68.51
Vested (in shares)	265,918	194,991	36,914
Nonvested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	601,012	170,994	258,393
Fair value per share on valuation date (in dollars per share)	$ 68.51	$ 78.97	$ 57.36
Vested (in shares)	261,875
Vested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	1,067
Vested (in shares)	261,875
Vest date fair value	$ 18,906	$ 14,270	$ 2,788

Share-Based Compensation - Su_3

Share-Based Compensation - Summary of Time-Based RSUs 1 (Details) - Time-Based Restricted Stock Units (RSUs) [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares)	214,131	228,095	130,784
Nonvested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of RSUs outstanding, beginning balance (in shares)	331,546
RSU weighted average fair value, beginning balance (in dollars per share)	$ 66.83
Granted (in shares)	437,216	142,101	173,747
Fair value per share on valuation date (in dollars per share)	$ 64.21	$ 74.91	$ 58.29
Vested (in shares)	187,209
Weighted average fair value, vested (in dollars per share)	$ 63.85
Issuance of dividend equivalents (in shares)	6,316
Weighted average fair value, issuance of dividend equivalents (in dollars per share)	$ 71.75
Forfeited (in shares)	(1,090)
Weighted average fair value, forfeited (in dollars per share)	$ 70.62
Number of RSUs outstanding, ending balance (in shares)	586,779	331,546
RSU weighted average fair value, ending balance (in dollars per share)	$ 65.87	$ 66.83
Vested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested RSUs, beginning balance	1,080,928
Granted (in shares)	0
Vested (in shares)	187,209
Settled (in shares)	(202,536)
Issuance of dividend equivalents (in shares)	26,922
Forfeited (in shares)	0
Canceled (in shares)	(3,435)
Vested RSUs, ending balance	1,089,088	1,080,928
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total RSUs, beginning balance (in shares)	1,412,474
Granted (in shares)	437,216
Vested (in shares)	0
Settled (in shares)	(202,536)
Issuance of dividend equivalents (in shares)	33,238
Forfeited (in shares)	(1,090)
Canceled (in shares)	(3,435)
Total RSUs, ending balance (in shares)	1,675,867	1,412,474
Kilroy Realty 2006 Incentive Award Plan [Member] | Vested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Settled (in shares)	(85,598)

Share-Based Compensation - Su_4

Share-Based Compensation - Summary of Time-Based RSUs 2 (Details) - Time-Based Restricted Stock Units (RSUs) [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares)	(214,131)	(228,095)	(130,784)
Nonvested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	437,216	142,101	173,747
Fair value per share on valuation date (in dollars per share)	$ 64.21	$ 74.91	$ 58.29
Vested (in shares)	(187,209)
Vested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	0
Vested (in shares)	(187,209)
Vest date fair value	$ 14,768	$ 16,735	$ 8,438

Share-Based Compensation - Su_5

Share-Based Compensation - Summary of Nonvested Restricted Stock 1 (Details) - Restricted Stock [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	0	0	0
RSU weighted average fair value, beginning balance (in dollars per share)	$ 55.23
Weighted average grant date fair value, transferred from time-based RSUs (in dollars per share)	0
Weighted average fair value, vested (in dollars per share)	55.23
RSU weighted average fair value, ending balance (in dollars per share)	$ 0	$ 55.23
Nonvested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of RSUs outstanding, beginning balance (in shares)	22,884
Granted (in shares)	0
Number of RSUs outstanding, ending balance (in shares)	0	22,884
Vested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares)	(22,884)	(24,261)	(24,262)
Repurchase of common stock and restricted stock units (in shares)		9,637

Share-Based Compensation - Su_6

Share-Based Compensation - Summary of Nonvested Restricted Stock 2 (Details) - Restricted Stock [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	0	0	0
Fair value per share on valuation date (in dollars per share)	$ 0	$ 0	$ 0
Vest date fair value	$ 1,652	$ 1,781	$ 1,527
Vested Restricted Stock Units RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares)	(22,884)	(24,261)	(24,262)

Share-Based Compensation - Shar

Share-Based Compensation - Share-Based Compensation Cost Recorded During the Period and Other Compensation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Allocated share-based compensation expense	$ 35.9	$ 26.3	$ 26.6
Share-based compensation costs	8	$ 7.3	$ 5.6
Unrecognized compensation costs	$ 60.5
Cost not yet recognized, period for recognition	3 years
Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash retirement benefit, scenario one	$ 13.2
Cash retirement benefit, scenario two	16.2
Compensation expense	$ 12.1

Employee Benefit Plans - Narrat

Employee Benefit Plans - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2007
Retirement Benefits [Abstract]
Eligibility period for 401K savings plan, period	3 months
401(k) plan, maximum participant deferral percent	60.00%
401(k) plan, employer match per dollar of participant contribution	$ 0.50
401(k) plan, maximum employer match percentage	10.00%
401(k) plan, contributions made	$ 1,500,000	$ 1,300,000	$ 1,200,000
Deferred Compensation, maximum participant deferral percent				70.00%
Deferred Compensation, maximum director fees and bonuses that may be deferred (percent)				100.00%
Deferred Compensation, mandatory Company contributions as percentage of gross monthly salary (percent)				10.00%
Deferred Compensation, liability under Plan	$ 21,700,000	$ 20,600,000

Future Minimum Rent - Future Co

Future Minimum Rent - Future Contractual Minimum Rent (Details) $ in Thousands	Dec. 31, 2018USD ($)
Future contractual minimum rent under operating lease
2,019	$ 566,783
2,020	632,875
2,021	631,835
2,022	620,684
2,023	586,371
Thereafter	3,240,143
Total	$ 6,278,691

Commitments and Contingencies -

Commitments and Contingencies - Minimum Commitment Under Ground Leases (Details) $ in Thousands	Dec. 31, 2018USD ($)
Summary of minimum commitment
2,019	$ 5,154
2,020	5,154
2,021	5,154
2,022	5,154
2,023	5,154
Thereafter	233,619
Total	$ 259,389

Commitments and Contingencies_2

Commitments and Contingencies - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)ground_lease_extension_options	Dec. 31, 2016USD ($)	Dec. 31, 2017USD ($)
Long-term Purchase Commitment [Line Items]
Commitments for contracts and executed leases, operating and redevelopment and development properties	$ 960.1
Period after which ground lease rentals are adjusted based on fair market value and the Consumer Price Index	5 years
Annual ground lease rental obligations limit	$ 1
Duration of ground lease prior to increase five years	5 years
Average annual percentage rent for previous five years (percent)	50.00%
Duration of ground lease prior to increase ten years	10 years
Average annual percentage rent for previous ten years (percent)	60.00%
Ten year ground lease extension option [Member]
Long-term Purchase Commitment [Line Items]
Number of extension options | ground_lease_extension_options	3
Ground lease extension option term	10 years
Forty-five year ground lease extension option [Member]
Long-term Purchase Commitment [Line Items]
Number of extension options | ground_lease_extension_options	1
Ground lease extension option term	45 years
Property damage litigation case [Member]
Long-term Purchase Commitment [Line Items]
Proceeds from legal settlements		$ 5
Environmental matters [Member]
Long-term Purchase Commitment [Line Items]
Accrued environmental remediation liabilities	$ 83.2		$ 28.3

Fair Value Measurements and D_3

Fair Value Measurements and Disclosures - Assets and Liabilities Reported at Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair value adjustment of marketable securities and deferred compensation plan liability
Net (loss) gain on marketable securities	$ (1,851)	$ 3,023	$ 1,130
Fair value, measurements, recurring [Member] | Fair Value (Level 1) [Member]
Assets and Liabilities Reported at Fair Value
Marketable securities	$ 21,779	$ 20,674

Fair Value Measurements and D_4

Fair Value Measurements and Disclosures - Financial Instruments Disclosed at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Carrying value [Member] | Secured debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value disclosure	$ 335,531	$ 340,800
Carrying value [Member] | Unsecured debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value disclosure	2,552,070	2,006,263
Carrying value [Member] | Unsecured line of credit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value disclosure	45,000	0
Fair value [Member] | Secured debt [Member] | Fair value (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value disclosure	335,885	346,858
Fair value [Member] | Unsecured debt [Member] | Fair value (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value disclosure	2,546,386	2,077,199
Fair value [Member] | Unsecured line of credit [Member] | Fair value (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value disclosure	$ 45,058	$ 0

Other Significant Events - Narr

Other Significant Events - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)tenant	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for bad debts		$ 5,685	$ 3,269	$ 0
Provisions for bad debts, increase (decrease)	$ (1,400)
Tenant One [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for bad debts	$ 7,000
Number of tenants | tenant		1

Net Income Available to Commo_5

Net Income Available to Common Stockholders Per Share of the Company - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income attributable to Kilroy Realty Corporation									$ 258,415	$ 164,612	$ 293,788
Preferred dividends and distributions					$ 0	$ (4,552)	$ (1,615)	$ (7,196)	0	(13,363)	(13,250)
Allocation to participating securities									(2,004)	(1,975)	(3,839)
Numerator for basic and diluted net income available to common stockholders									$ 256,411	$ 149,274	$ 276,699
Denominator:
Basic weighted average vested shares/units outstanding (in shares/units)									99,972,359	98,113,561	92,342,483
Effect of dilutive securities (in shares)									510,006	613,770	680,551
Diluted weighted average vested shares and common stock/ unit equivalents outstanding (in shares/units)									100,482,365	98,727,331	93,023,034
Basic earnings per share:
Net income available to common stockholders per share - basic (in dollars per share)	$ 1.59	$ 0.34	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.27	$ 2.56	$ 1.52	$ 3
Diluted earnings per share:
Net income available to common stockholders per share - diluted (in dollars per share)	$ 1.58	$ 0.33	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.26	$ 2.55	$ 1.51	$ 2.97

Net Income Available to Commo_6

Net Income Available to Common Unitholders Per Unit of the Operating Partnership - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income attributable to Kilroy Realty, L.P.									$ 258,415	$ 164,612	$ 293,788
Preferred dividends and distributions					$ 0	$ (4,552)	$ (1,615)	$ (7,196)	0	(13,363)	(13,250)
Allocation to participating securities (1)									(2,004)	(1,975)	(3,839)
Numerator for basic and diluted net income available to common stockholders									$ 256,411	$ 149,274	$ 276,699
Denominator:
Basic weighted average vested shares/units outstanding (in shares/units)									99,972,359	98,113,561	92,342,483
Effect of dilutive securities (in units)									510,006	613,770	680,551
Diluted weighted average vested shares and common stock/ unit equivalents outstanding (in shares/units)									100,482,365	98,727,331	93,023,034
Basic earnings per unit:
Net income available to common unitholders per unit (in dollars per unit)	$ 1.59	$ 0.34	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.27	$ 2.56	$ 1.52	$ 3
Diluted earnings per unit:
Net income available to common unitholders per unit (in dollars per unit)	1.58	0.33	0.27	0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.26	$ 2.55	$ 1.51	$ 2.97
Kilroy Realty L.P. [Member]
Numerator:
Net income attributable to Kilroy Realty, L.P.									$ 263,210	$ 167,440	$ 300,063
Preferred dividends and distributions					$ 0	$ (4,552)	$ (1,615)	$ (7,196)	0	(13,363)	(13,250)
Allocation to participating securities (1)									(2,004)	(1,975)	(3,839)
Numerator for basic and diluted net income available to common stockholders									$ 261,206	$ 152,102	$ 282,974
Denominator:
Basic weighted average vested shares/units outstanding (in shares/units)									102,025,276	100,246,567	94,771,688
Effect of dilutive securities (in units)									510,006	613,770	680,551
Diluted weighted average vested shares and common stock/ unit equivalents outstanding (in shares/units)									102,535,282	100,860,337	95,452,239
Basic earnings per unit:
Net income available to common unitholders per unit (in dollars per unit)	1.58	0.34	0.27	0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.26	$ 2.56	$ 1.52	$ 2.99
Diluted earnings per unit:
Net income available to common unitholders per unit (in dollars per unit)	$ 1.57	$ 0.33	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.26	$ 2.55	$ 1.51	$ 2.96

Supplemental Cash Flow Inform_4

Supplemental Cash Flow Information of the Company - Supplemental Cash Flow (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $65,627, $44,757, and $47,675 as of December 31, 2018, 2017 and 2016, respectively	$ 44,697	$ 67,336	$ 54,295
Capitalized interest	65,627	44,757	47,675
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development and redevelopment properties	158,626	116,089	62,589
Tenant improvements funded directly by tenants	13,968	15,314	18,050
Assumption of other assets and liabilities in connection with operating and development property acquisitions, net	40,624	1,443	5,863
Accrual for receivable related to development properties	0	0	1,350
NON-CASH FINANCING TRANSACTIONS:
Accrual of dividends and distributions payable to common stockholders and common unitholders	47,559	43,448	220,650
Exchange of common units of the Operating Partnership into shares of the Company’s common stock	1,962	10,939	8,893
Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders	0	0	1,656
Issuance of common units of the Operating Partnership in connection with an acquisition			48,033
Secured debt assumed by buyers in connection with land disposition	$ 0	$ 0	$ 2,322

Supplemental Cash Flow Inform_5

Supplemental Cash Flow Information of the Company - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 51,604	$ 57,649	$ 193,418	$ 56,508
Restricted cash	119,430	9,149	56,711	696
Cash and cash equivalents and restricted cash	$ 171,034	$ 66,798	$ 250,129	$ 57,204

Supplemental Cash Flow Inform_6

Supplemental Cash Flow Information of the Operating Partnership - Supplemental Cash Flow (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $65,627, $44,757, and $47,675 as of December 31, 2018, 2017 and 2016, respectively	$ 44,697	$ 67,336	$ 54,295
Capitalized interest	65,627	44,757	47,675
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development and redevelopment properties	158,626	116,089	62,589
Tenant improvements funded directly by tenants	13,968	15,314	18,050
Assumption of other assets and liabilities in connection with operating and development property acquisitions, net	40,624	1,443	5,863
Accrual for receivable related to development properties	0	0	1,350
NON-CASH FINANCING TRANSACTIONS:
Accrual of dividends and distributions payable to common stockholders and common unitholders	47,559	43,448	220,650
Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders	0	0	1,656
Issuance of common units in connection with a development property acquisition			48,033
Secured debt assumed by buyers in connection with land disposition	0	0	2,322
Kilroy Realty L.P. [Member]
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $65,627, $44,757, and $47,675 as of December 31, 2018, 2017 and 2016, respectively	44,697	67,336	54,295
Capitalized interest	65,627	44,757	47,675
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development and redevelopment properties	158,626	116,089	62,589
Tenant improvements funded directly by tenants	13,968	15,314	18,050
Assumption of other assets and liabilities in connection with operating and development property acquisitions, net	40,624	1,443	5,863
Accrual for receivable related to development properties	0	0	1,350
NON-CASH FINANCING TRANSACTIONS:
Accrual of dividends and distributions payable to common stockholders and common unitholders	47,559	43,448	220,650
Accrual of dividends and distributions payable to preferred stockholders and preferred unitholders	0	0	1,656
Issuance of common units in connection with a development property acquisition	0	0	48,033
Secured debt assumed by buyers in connection with land disposition	$ 0	$ 0	$ 2,322

Supplemental Cash Flow Inform_7

Supplemental Cash Flow Information of the Operating Partnership - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Significant Noncash Transactions [Line Items]
Cash and cash equivalents	$ 51,604	$ 57,649	$ 193,418	$ 56,508
Restricted cash	119,430	9,149	56,711	696
Cash and cash equivalents and restricted cash	171,034	66,798	250,129	57,204
Kilroy Realty L.P. [Member]
Other Significant Noncash Transactions [Line Items]
Cash and cash equivalents	51,604	57,649	193,418	56,508
Restricted cash	119,430	9,149	56,711	696
Cash and cash equivalents and restricted cash	$ 171,034	$ 66,798	$ 250,129	$ 57,204

Tax Treatment of Distribution_2

Tax Treatment of Distributions - Dividends (Details) - $ / shares	Jan. 13, 2017	Dec. 31, 2016	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Dividends declared per common share (in dollars per share)			$ 0.375	$ 0.375	$ 1.79000	$ 1.65	$ 3.375
Dividends paid per common share (in dollars per share)	$ 0.313
Common Stock [Member]
Class of Stock [Line Items]
Dividends declared per common share (in dollars per share)				2.275	1.790	1.650	3.375
Less: Dividends declared in the current year and paid in the following year (in dollars per share)					(0.455)	(0.425)	(2.275)
Add: Dividends declared in the prior year and paid in the current year (in dollars per share)					0.425	2.275	0.350
Dividends paid per common share (in dollars per share)					$ 1.760	$ 3.500	$ 1.450
Special Dividend [Member]
Class of Stock [Line Items]
Dividends declared per common share (in dollars per share)				$ 1.90
Dividends paid per common share (in dollars per share)		$ 1.587

Tax Treatment of Distribution_3

Tax Treatment of Distributions - Dividends Tax Treatment (Details) - $ / shares	Aug. 15, 2017	Mar. 30, 2017	Jan. 13, 2017	Aug. 31, 2012	Mar. 31, 2012	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)			$ 0.313
Capital gains, federal statutory tax rate						20.00%		20.00%
Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)						$ 1.760	$ 3.500	$ 1.450
Series G Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Preferred stock, dividend rate		6.875%			6.875%
Series H Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Preferred stock, dividend rate	6.375%			6.375%
Tax treatment, Ordinary income [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)						$ 1.474	$ 1.356	$ 1.500
Dividends paid per common share, percentage						83.73%	70.87%	49.40%
Tax treatment, Ordinary income [Member] | Series G Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per preferred share (in dollars per share)							$ 0.371	$ 0.848
Dividend paid per preferred share, percentage							86.43%	49.31%
Tax treatment, Ordinary income [Member] | Series H Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per preferred share (in dollars per share)							$ 1.033	$ 0.786
Dividend paid per preferred share, percentage							86.43%	49.31%
Tax treatment, Qualified dividend [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)						$ 0.003	$ 0.002	$ 0.002
Dividends paid per common share, percentage						0.19%	0.11%	0.06%
Tax treatment, Qualified dividend [Member] | Series G Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per preferred share (in dollars per share)							$ 0.001	$ 0.001
Dividend paid per preferred share, percentage							0.14%	0.06%
Tax treatment, Qualified dividend [Member] | Series H Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per preferred share (in dollars per share)							$ 0.002	$ 0.001
Dividend paid per preferred share, percentage							0.14%	0.06%
Tax treatment, Return of capital [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)						$ 0.275	$ 0.344	$ 0
Dividends paid per common share, percentage						15.64%	18.00%	0.00%
Tax treatment, Capital gains [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)						$ 0.008	$ 0	$ 1.212
Dividends paid per common share, percentage						0.44%	0.00%	39.89%
Tax treatment, Capital gains [Member] | Series G Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per preferred share (in dollars per share)							$ 0	$ 0.687
Dividend paid per preferred share, percentage							0.00%	39.97%
Tax treatment, Capital gains [Member] | Series H Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per preferred share (in dollars per share)							$ 0	$ 0.637
Dividend paid per preferred share, percentage							0.00%	39.97%
Tax treatment, Unrecaptured section 1250 gains [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)						$ 0	$ 0.211	$ 0.323
Dividends paid per common share, percentage						0.00%	11.02%	10.65%
Tax treatment, Unrecaptured section 1250 gains [Member] | Series G Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per preferred share (in dollars per share)							$ 0.058	$ 0.183
Dividend paid per preferred share, percentage							13.43%	10.66%
Tax treatment, Unrecaptured section 1250 gains [Member] | Series H Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per preferred share (in dollars per share)							$ 0.160	$ 0.170
Dividend paid per preferred share, percentage							13.43%	10.66%
Tax treatment [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)						$ 1.760	$ 1.913	$ 3.037
Dividends paid per common share, percentage						100.00%	100.00%	100.00%
Tax treatment [Member] | Series G Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per preferred share (in dollars per share)							$ 0.430	$ 1.719
Dividend paid per preferred share, percentage							100.00%	100.00%
Tax treatment [Member] | Series H Preferred Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per preferred share (in dollars per share)							$ 1.195	$ 1.594
Dividend paid per preferred share, percentage							100.00%	100.00%

Quarterly Financial Informati_5

Quarterly Financial Information of the Company (Unaudited) - Summarized Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 190,842	$ 186,562	$ 187,072	$ 182,822	$ 177,561	$ 181,534	$ 180,598	$ 179,308	$ 747,298	$ 719,001	$ 642,572
Net income	166,890	38,310	31,755	40,971	32,540	75,488	35,306	37,281	277,926	180,615	303,798
Net income attributable to Kilroy Realty Corporation	160,220	34,400	27,549	36,246	28,529	71,110	31,448	33,525	258,415	164,612	293,788
Preferred dividends and distributions					0	(4,552)	(1,615)	(7,196)	0	(13,363)	(13,250)
Net income available to common stockholders	$ 160,220	$ 34,400	$ 27,549	$ 36,246	$ 28,529	$ 66,558	$ 29,833	$ 26,329	$ 258,415	$ 151,249	$ 280,538
Net income available to common stockholders per share/ unit—basic (dollars per share/ unit)	$ 1.59	$ 0.34	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.27	$ 2.56	$ 1.52	$ 3
Net income available to common stockholders per share/ unit—diluted (dollars per share/ unit)	$ 1.58	$ 0.33	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.26	$ 2.55	$ 1.51	$ 2.97

Quarterly Financial Informati_6

Quarterly Financial Information of the Operating Partnership (Unaudited) - Summarized Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues	$ 190,842	$ 186,562	$ 187,072	$ 182,822	$ 177,561	$ 181,534	$ 180,598	$ 179,308	$ 747,298	$ 719,001	$ 642,572
Net income	166,890	38,310	31,755	40,971	32,540	75,488	35,306	37,281	277,926	180,615	303,798
Net income attributable to the Operating Partnership	160,220	34,400	27,549	36,246	28,529	71,110	31,448	33,525	258,415	164,612	293,788
Total preferred distributions					0	(4,552)	(1,615)	(7,196)	0	(13,363)	(13,250)
Net income available to common stockholders	$ 160,220	$ 34,400	$ 27,549	$ 36,246	$ 28,529	$ 66,558	$ 29,833	$ 26,329	$ 258,415	$ 151,249	$ 280,538
Net income available to common stockholders per share/ unit—basic (dollars per share/ unit)	$ 1.59	$ 0.34	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.27	$ 2.56	$ 1.52	$ 3
Net income available to common stockholders per share/ unit—diluted (dollars per share/ unit)	$ 1.58	$ 0.33	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.26	$ 2.55	$ 1.51	$ 2.97
Kilroy Realty L.P. [Member]
Revenues	$ 190,842	$ 186,562	$ 187,072	$ 182,822	$ 177,561	$ 181,534	$ 180,598	$ 179,308	$ 747,298	$ 719,001	$ 642,572
Net income	166,890	38,310	31,755	40,971	32,540	75,488	35,306	37,281	277,926	180,615	303,798
Net income attributable to the Operating Partnership	163,309	34,993	28,015	36,893	29,013	72,402	31,971	34,054	263,210	167,440	300,063
Total preferred distributions					0	(4,552)	(1,615)	(7,196)	0	(13,363)	(13,250)
Net income available to common stockholders	$ 163,309	$ 34,993	$ 28,015	$ 36,893	$ 29,013	$ 67,850	$ 30,356	$ 26,858	$ 263,210	$ 154,077	$ 286,813
Net income available to common stockholders per share/ unit—basic (dollars per share/ unit)	$ 1.58	$ 0.34	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.26	$ 2.56	$ 1.52	$ 2.99
Net income available to common stockholders per share/ unit—diluted (dollars per share/ unit)	$ 1.57	$ 0.33	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.26	$ 2.55	$ 1.51	$ 2.96

Subsequent Events - Narrative (

Subsequent Events - Narrative (Details) - USD ($) $ in Thousands	Feb. 11, 2019	Jan. 29, 2019	Jan. 15, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 01, 2019
Subsequent Event [Line Items]
Payments of dividends, common stock				$ 179,411	$ 340,697	$ 137,444
Repayments of secured debt				$ 3,584	130,371	74,140
Kilroy Realty 2006 Incentive Award Plan [Member]
Subsequent Event [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares available for grant				600,000
Subsequent event [Member]
Subsequent Event [Line Items]
Payments of dividends, common stock			$ 47,500
Subsequent event [Member] | Kilroy Realty 2006 Incentive Award Plan [Member] | Time-Based Restricted Stock Units (RSUs) [Member] | Chief Executive Officer [Member]
Subsequent Event [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares available for grant		144,982
Subsequent event [Member] | Kilroy Realty 2006 Incentive Award Plan [Member] | Market measure-based Restricted Stock Units (RSUs) [Member] | Chief Executive Officer [Member]
Subsequent Event [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares available for grant							143,396
Share-based compensation arrangement by share-based payment award, award requisite service period		3 years
Kilroy Realty L.P. [Member]
Subsequent Event [Line Items]
Payments of dividends, common stock				$ 179,411	340,697	137,444
Repayments of secured debt				$ 3,584	$ 130,371	$ 74,140
Secured debt [Member] | 6.05% Mortgage Payable Due June 1, 2019 [Member] | Kilroy Realty L.P. [Member] | Subsequent event [Member]
Subsequent Event [Line Items]
Repayments of secured debt	$ 74,300

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts - Allowances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Notes receivable, valuation allowance	$ 2,900
Uncollectible tenant receivables [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	2,309	$ 1,712	$ 2,080
Charged to Costs and Expenses (1)	2,604	1,517	0
Recoveries (Deductions)	(274)	(920)	(368)
Balance at End of Period	4,639	2,309	1,712
Allowance for deferred rent [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	3,238	1,524	1,882
Charged to Costs and Expenses (1)	165	1,752	0
Recoveries (Deductions)	(64)	(38)	(358)
Balance at End of Period	$ 3,339	$ 3,238	$ 1,524

Schedule III - Real Estate an_2

Schedule III - Real Estate and Accumulated Depreciation - Schedule of Real Estate and Accumulated Depreciation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)ft²	Dec. 21, 2018ft²	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, encumbrances	$ 335,811
Initial cost, land and improvements	2,058,007
Initial cost, buildings and Improvements	2,777,476
Costs capitalized subsequent to acquisition/ improvement	3,591,149
Land and improvements, gross	2,100,230
Buildings and improvements, gross	6,326,402
Land and improvements and buildings and improvements, gross	8,426,632
Accumulated depreciation	$ 1,391,368		$ 1,264,162	$ 1,139,853	$ 994,241
Rentable square feet | ft²	13,232,580
345 Brannan St., San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Rentable square feet | ft²		110,030
Office Building [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, encumbrances	$ 335,811
Initial cost, land and improvements	1,117,915
Initial cost, buildings and Improvements	2,777,476
Costs capitalized subsequent to acquisition/ improvement	2,472,731
Land and improvements, gross	1,160,138
Buildings and improvements, gross	5,207,984
Land and improvements and buildings and improvements, gross	6,368,122
Accumulated depreciation	$ 1,391,368
Rentable square feet | ft²	13,232,580
Office Building [Member] | 2829 Townsgate Rd., Thousand Oaks, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 5,248
Initial cost, buildings and Improvements	8,001
Costs capitalized subsequent to acquisition/ improvement	8,267
Land and improvements, gross	5,248
Buildings and improvements, gross	16,268
Land and improvements and buildings and improvements, gross	21,516
Accumulated depreciation	$ 11,862
Depreciation life	35 years
Rentable square feet | ft²	84,098
Office Building [Member] | 2240 E. Imperial Highway, El Segundo, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 1,044
Initial cost, buildings and Improvements	11,763
Costs capitalized subsequent to acquisition/ improvement	29,509
Land and improvements, gross	1,048
Buildings and improvements, gross	41,268
Land and improvements and buildings and improvements, gross	42,316
Accumulated depreciation	$ 25,671
Depreciation life	35 years
Rentable square feet | ft²	122,870
Office Building [Member] | 2250 E. Imperial Highway, El Segundo, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 2,579
Initial cost, buildings and Improvements	29,062
Costs capitalized subsequent to acquisition/ improvement	36,148
Land and improvements, gross	2,547
Buildings and improvements, gross	65,242
Land and improvements and buildings and improvements, gross	67,789
Accumulated depreciation	$ 52,858
Depreciation life	35 years
Rentable square feet | ft²	298,728
Office Building [Member] | 2260 E. Imperial Highway, El Segundo, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 2,518
Initial cost, buildings and Improvements	28,370
Costs capitalized subsequent to acquisition/ improvement	36,672
Land and improvements, gross	2,547
Buildings and improvements, gross	65,013
Land and improvements and buildings and improvements, gross	67,560
Accumulated depreciation	$ 14,064
Depreciation life	35 years
Rentable square feet | ft²	298,728
Office Building [Member] | 909 N. Pacific Coast Highway, El Segundo, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 3,577
Initial cost, buildings and Improvements	34,042
Costs capitalized subsequent to acquisition/ improvement	48,056
Land and improvements, gross	3,577
Buildings and improvements, gross	82,098
Land and improvements and buildings and improvements, gross	85,675
Accumulated depreciation	$ 38,602
Depreciation life	35 years
Rentable square feet | ft²	244,136
Office Building [Member] | 999 N. Pacific Coast Highway, El Segundo, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 1,407
Initial cost, buildings and Improvements	34,326
Costs capitalized subsequent to acquisition/ improvement	16,497
Land and improvements, gross	1,407
Buildings and improvements, gross	50,823
Land and improvements and buildings and improvements, gross	52,230
Accumulated depreciation	$ 23,178
Depreciation life	35 years
Rentable square feet | ft²	128,588
Office Building [Member] | 6115 W. Sunset Blvd., Los Angeles, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 1,313
Initial cost, buildings and Improvements	3
Costs capitalized subsequent to acquisition/ improvement	16,458
Land and improvements, gross	2,455
Buildings and improvements, gross	15,319
Land and improvements and buildings and improvements, gross	17,774
Accumulated depreciation	$ 1,483
Depreciation life	35 years
Rentable square feet | ft²	26,105
Office Building [Member] | 6121 W. Sunset Blvd., Los Angeles, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 11,120
Initial cost, buildings and Improvements	4,256
Costs capitalized subsequent to acquisition/ improvement	43,952
Land and improvements, gross	8,703
Buildings and improvements, gross	50,625
Land and improvements and buildings and improvements, gross	59,328
Accumulated depreciation	$ 5,631
Depreciation life	35 years
Rentable square feet | ft²	91,173
Office Building [Member] | 1525 N. Gower Street, Los Angeles, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 1,318
Initial cost, buildings and Improvements	3
Costs capitalized subsequent to acquisition/ improvement	9,642
Land and improvements, gross	1,318
Buildings and improvements, gross	9,645
Land and improvements and buildings and improvements, gross	10,963
Accumulated depreciation	$ 870
Depreciation life	35 years
Rentable square feet | ft²	9,610
Office Building [Member] | 1575 N. Gower Street, Los Angeles, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 22,153
Initial cost, buildings and Improvements	51
Costs capitalized subsequent to acquisition/ improvement	119,406
Land and improvements, gross	22,153
Buildings and improvements, gross	119,457
Land and improvements and buildings and improvements, gross	141,610
Accumulated depreciation	$ 8,149
Depreciation life	35 years
Rentable square feet | ft²	251,245
Office Building [Member] | 1500 N. El Centro Avenue, Los Angeles, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 9,235
Initial cost, buildings and Improvements	21
Costs capitalized subsequent to acquisition/ improvement	58,582
Land and improvements, gross	9,235
Buildings and improvements, gross	58,603
Land and improvements and buildings and improvements, gross	67,838
Accumulated depreciation	$ 4,026
Depreciation life	35 years
Rentable square feet | ft²	104,504
Office Building [Member] | 1550 N. El Centro Avenue, Los Angeles, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 16,970
Initial cost, buildings and Improvements	39
Costs capitalized subsequent to acquisition/ improvement	135,583
Land and improvements, gross	16,970
Buildings and improvements, gross	135,622
Land and improvements and buildings and improvements, gross	152,592
Accumulated depreciation	$ 9,911
Depreciation life	35 years
Office Building [Member] | 6255 W. Sunset Blvd., Los Angeles, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 18,111
Initial cost, buildings and Improvements	60,320
Costs capitalized subsequent to acquisition/ improvement	44,535
Land and improvements, gross	18,111
Buildings and improvements, gross	104,855
Land and improvements and buildings and improvements, gross	122,966
Accumulated depreciation	$ 29,278
Depreciation life	35 years
Rentable square feet | ft²	323,920
Office Building [Member] | 3750 Kilroy Airport Way, Long Beach, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, buildings and Improvements	$ 1,941
Costs capitalized subsequent to acquisition/ improvement	11,153
Buildings and improvements, gross	13,094
Land and improvements and buildings and improvements, gross	13,094
Accumulated depreciation	$ 10,395
Depreciation life	35 years
Rentable square feet | ft²	10,457
Office Building [Member] | 3760 Kilroy Airport Way, Long Beach, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, buildings and Improvements	$ 17,467
Costs capitalized subsequent to acquisition/ improvement	13,714
Buildings and improvements, gross	31,181
Land and improvements and buildings and improvements, gross	31,181
Accumulated depreciation	$ 25,635
Depreciation life	35 years
Rentable square feet | ft²	165,278
Office Building [Member] | 3780 Kilroy Airport Way, Long Beach, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, buildings and Improvements	$ 22,319
Costs capitalized subsequent to acquisition/ improvement	23,008
Buildings and improvements, gross	45,327
Land and improvements and buildings and improvements, gross	45,327
Accumulated depreciation	$ 37,365
Depreciation life	35 years
Rentable square feet | ft²	219,777
Office Building [Member] | 3800 Kilroy Airport Way, Long Beach, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, buildings and Improvements	$ 19,408
Costs capitalized subsequent to acquisition/ improvement	20,838
Buildings and improvements, gross	40,246
Land and improvements and buildings and improvements, gross	40,246
Accumulated depreciation	$ 23,575
Depreciation life	35 years
Rentable square feet | ft²	192,476
Office Building [Member] | 3840 Kilroy Airport Way, Long Beach, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, buildings and Improvements	$ 13,586
Costs capitalized subsequent to acquisition/ improvement	10,364
Buildings and improvements, gross	23,950
Land and improvements and buildings and improvements, gross	23,950
Accumulated depreciation	$ 15,417
Depreciation life	35 years
Rentable square feet | ft²	136,026
Office Building [Member] | 3880 Kilroy Airport Way, Long Beach, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, buildings and Improvements	$ 9,704
Costs capitalized subsequent to acquisition/ improvement	11,277
Buildings and improvements, gross	20,981
Land and improvements and buildings and improvements, gross	20,981
Accumulated depreciation	$ 3,820
Depreciation life	35 years
Rentable square feet | ft²	96,035
Office Building [Member] | 3900 Kilroy Airport Way, Long Beach, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, buildings and Improvements	$ 12,615
Costs capitalized subsequent to acquisition/ improvement	11,983
Buildings and improvements, gross	24,598
Land and improvements and buildings and improvements, gross	24,598
Accumulated depreciation	$ 17,147
Depreciation life	35 years
Rentable square feet | ft²	129,893
Office Building [Member] | Kilroy Airport Center, Phase IV, Long Beach, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Costs capitalized subsequent to acquisition/ improvement	$ 4,997
Buildings and improvements, gross	4,997
Land and improvements and buildings and improvements, gross	4,997
Accumulated depreciation	$ 4,997
Depreciation life	35 years
Office Building [Member] | 8560 W. Sunset Blvd, West Hollywood, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 9,720
Initial cost, buildings and Improvements	50,956
Costs capitalized subsequent to acquisition/ improvement	600
Land and improvements, gross	9,720
Buildings and improvements, gross	51,556
Land and improvements and buildings and improvements, gross	61,276
Accumulated depreciation	$ 4,209
Depreciation life	35 years
Rentable square feet | ft²	71,875
Office Building [Member] | 8570 W. Sunset Blvd, West Hollywood, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 31,693
Initial cost, buildings and Improvements	27,974
Costs capitalized subsequent to acquisition/ improvement	925
Land and improvements, gross	31,693
Buildings and improvements, gross	28,899
Land and improvements and buildings and improvements, gross	60,592
Accumulated depreciation	$ 2,085
Depreciation life	35 years
Rentable square feet | ft²	43,603
Office Building [Member] | 8580 W. Sunset Blvd, West Hollywood, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 10,013
Initial cost, buildings and Improvements	3,695
Costs capitalized subsequent to acquisition/ improvement	135
Land and improvements, gross	10,013
Buildings and improvements, gross	3,830
Land and improvements and buildings and improvements, gross	13,843
Accumulated depreciation	$ 264
Depreciation life	35 years
Rentable square feet | ft²	7,126
Office Building [Member] | 8590 W. Sunset Blvd, West Hollywood, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 39,954
Initial cost, buildings and Improvements	27,884
Costs capitalized subsequent to acquisition/ improvement	1,092
Land and improvements, gross	39,954
Buildings and improvements, gross	28,976
Land and improvements and buildings and improvements, gross	68,930
Accumulated depreciation	$ 2,267
Depreciation life	35 years
Rentable square feet | ft²	56,095
Office Building [Member] | 12100 W. Olympic Blvd., Los Angeles, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, encumbrances	$ 170,000
Initial cost, land and improvements	352
Initial cost, buildings and Improvements	45,611
Costs capitalized subsequent to acquisition/ improvement	18,518
Land and improvements, gross	9,633
Buildings and improvements, gross	54,848
Land and improvements and buildings and improvements, gross	64,481
Accumulated depreciation	$ 27,316
Depreciation life	35 years
Rentable square feet | ft²	152,048
Office Building [Member] | 12200 W. Olympic Blvd., Los Angeles, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 4,329
Initial cost, buildings and Improvements	35,488
Costs capitalized subsequent to acquisition/ improvement	23,707
Land and improvements, gross	3,977
Buildings and improvements, gross	59,547
Land and improvements and buildings and improvements, gross	63,524
Accumulated depreciation	$ 37,257
Depreciation life	35 years
Rentable square feet | ft²	150,832
Office Building [Member] | 12233 Olympic Blvd., Los Angeles, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 22,100
Initial cost, buildings and Improvements	53,170
Costs capitalized subsequent to acquisition/ improvement	3,986
Land and improvements, gross	22,100
Buildings and improvements, gross	57,156
Land and improvements and buildings and improvements, gross	79,256
Accumulated depreciation	$ 11,832
Depreciation life	35 years
Rentable square feet | ft²	151,029
Office Building [Member] | 12312 W. Olympic Blvd., Los Angeles, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 3,325
Initial cost, buildings and Improvements	12,202
Costs capitalized subsequent to acquisition/ improvement	11,341
Land and improvements, gross	3,399
Buildings and improvements, gross	23,469
Land and improvements and buildings and improvements, gross	26,868
Accumulated depreciation	$ 12,017
Depreciation life	35 years
Rentable square feet | ft²	76,644
Office Building [Member] | 1633 26th St., Santa Monica, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 2,080
Initial cost, buildings and Improvements	6,672
Costs capitalized subsequent to acquisition/ improvement	3,139
Land and improvements, gross	2,040
Buildings and improvements, gross	9,851
Land and improvements and buildings and improvements, gross	11,891
Accumulated depreciation	$ 6,908
Depreciation life	35 years
Rentable square feet | ft²	43,857
Office Building [Member] | 2100/2110 Colorado Ave., Santa Monica, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, encumbrances	$ 91,332
Initial cost, land and improvements	5,474
Initial cost, buildings and Improvements	26,087
Costs capitalized subsequent to acquisition/ improvement	14,620
Land and improvements, gross	5,476
Buildings and improvements, gross	40,705
Land and improvements and buildings and improvements, gross	46,181
Accumulated depreciation	$ 24,031
Depreciation life	35 years
Rentable square feet | ft²	102,864
Office Building [Member] | 3130 Wilshire Blvd., Santa Monica, [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 8,921
Initial cost, buildings and Improvements	6,579
Costs capitalized subsequent to acquisition/ improvement	15,992
Land and improvements, gross	9,188
Buildings and improvements, gross	22,304
Land and improvements and buildings and improvements, gross	31,492
Accumulated depreciation	$ 14,674
Depreciation life	35 years
Rentable square feet | ft²	90,074
Office Building [Member] | 501 Santa Monica Blvd., Santa Monica, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 4,547
Initial cost, buildings and Improvements	12,044
Costs capitalized subsequent to acquisition/ improvement	14,129
Land and improvements, gross	4,551
Buildings and improvements, gross	26,169
Land and improvements and buildings and improvements, gross	30,720
Accumulated depreciation	$ 15,614
Depreciation life	35 years
Rentable square feet | ft²	76,803
Office Building [Member] | 2211 Michelson, Irvine, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 9,319
Initial cost, buildings and Improvements	82,836
Costs capitalized subsequent to acquisition/ improvement	6,629
Land and improvements, gross	9,319
Buildings and improvements, gross	89,465
Land and improvements and buildings and improvements, gross	98,784
Accumulated depreciation	$ 27,097
Depreciation life	35 years
Rentable square feet | ft²	271,556
Office Building [Member] | 12225 El Camino Real, Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 1,700
Initial cost, buildings and Improvements	9,633
Costs capitalized subsequent to acquisition/ improvement	3,493
Land and improvements, gross	1,673
Buildings and improvements, gross	13,153
Land and improvements and buildings and improvements, gross	14,826
Accumulated depreciation	$ 8,905
Depreciation life	35 years
Rentable square feet | ft²	58,401
Office Building [Member] | 12235 El Camino Real, Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 1,507
Initial cost, buildings and Improvements	8,543
Costs capitalized subsequent to acquisition/ improvement	8,965
Land and improvements, gross	1,540
Buildings and improvements, gross	17,475
Land and improvements and buildings and improvements, gross	19,015
Accumulated depreciation	$ 9,681
Depreciation life	35 years
Rentable square feet | ft²	53,751
Office Building [Member] | 12340 El Camino Real, Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 4,201
Initial cost, buildings and Improvements	13,896
Costs capitalized subsequent to acquisition/ improvement	9,858
Land and improvements, gross	4,201
Buildings and improvements, gross	23,754
Land and improvements and buildings and improvements, gross	27,955
Accumulated depreciation	$ 11,257
Depreciation life	35 years
Rentable square feet | ft²	89,272
Office Building [Member] | 12390 El Camino Real, Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 3,453
Initial cost, buildings and Improvements	11,981
Costs capitalized subsequent to acquisition/ improvement	3,896
Land and improvements, gross	3,453
Buildings and improvements, gross	15,877
Land and improvements and buildings and improvements, gross	19,330
Accumulated depreciation	$ 8,995
Depreciation life	35 years
Rentable square feet | ft²	70,140
Office Building [Member] | 12348 High Bluff Dr., Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 1,629
Initial cost, buildings and Improvements	3,096
Costs capitalized subsequent to acquisition/ improvement	6,141
Land and improvements, gross	1,629
Buildings and improvements, gross	9,237
Land and improvements and buildings and improvements, gross	10,866
Accumulated depreciation	$ 6,206
Depreciation life	35 years
Rentable square feet | ft²	38,806
Office Building [Member] | 12400 High Bluff Dr., Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 15,167
Initial cost, buildings and Improvements	40,497
Costs capitalized subsequent to acquisition/ improvement	14,337
Land and improvements, gross	15,167
Buildings and improvements, gross	54,834
Land and improvements and buildings and improvements, gross	70,001
Accumulated depreciation	$ 27,243
Depreciation life	35 years
Rentable square feet | ft²	209,220
Office Building [Member] | 3579 Valley Centre Dr., Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 2,167
Initial cost, buildings and Improvements	6,897
Costs capitalized subsequent to acquisition/ improvement	7,449
Land and improvements, gross	2,858
Buildings and improvements, gross	13,655
Land and improvements and buildings and improvements, gross	16,513
Accumulated depreciation	$ 9,512
Depreciation life	35 years
Rentable square feet | ft²	52,418
Office Building [Member] | 3611 Valley Centre Dr., Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 4,184
Initial cost, buildings and Improvements	19,352
Costs capitalized subsequent to acquisition/ improvement	18,881
Land and improvements, gross	5,259
Buildings and improvements, gross	37,158
Land and improvements and buildings and improvements, gross	42,417
Accumulated depreciation	$ 24,251
Depreciation life	35 years
Rentable square feet | ft²	129,656
Office Building [Member] | 3661 Valley Centre Dr., Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 4,038
Initial cost, buildings and Improvements	21,144
Costs capitalized subsequent to acquisition/ improvement	16,178
Land and improvements, gross	4,725
Buildings and improvements, gross	36,635
Land and improvements and buildings and improvements, gross	41,360
Accumulated depreciation	$ 20,619
Depreciation life	35 years
Rentable square feet | ft²	128,364
Office Building [Member] | 3721 Valley Centre Dr., Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 4,297
Initial cost, buildings and Improvements	18,967
Costs capitalized subsequent to acquisition/ improvement	14,569
Land and improvements, gross	4,254
Buildings and improvements, gross	33,579
Land and improvements and buildings and improvements, gross	37,833
Accumulated depreciation	$ 15,893
Depreciation life	35 years
Rentable square feet | ft²	115,193
Office Building [Member] | 3811 Valley Centre Dr., Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 3,452
Initial cost, buildings and Improvements	16,152
Costs capitalized subsequent to acquisition/ improvement	20,105
Land and improvements, gross	4,457
Buildings and improvements, gross	35,252
Land and improvements and buildings and improvements, gross	39,709
Accumulated depreciation	$ 21,545
Depreciation life	35 years
Rentable square feet | ft²	112,067
Office Building [Member] | 12770 El Camino Real, Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 9,360
Initial cost, buildings and Improvements	0
Costs capitalized subsequent to acquisition/ improvement	33,628
Land and improvements, gross	9,360
Buildings and improvements, gross	33,628
Land and improvements and buildings and improvements, gross	42,988
Accumulated depreciation	$ 1,950
Depreciation life	35 years
Rentable square feet | ft²	73,032
Office Building [Member] | 12780 El Camino Real, Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 18,398
Initial cost, buildings and Improvements	54,954
Costs capitalized subsequent to acquisition/ improvement	14,775
Land and improvements, gross	18,398
Buildings and improvements, gross	69,729
Land and improvements and buildings and improvements, gross	88,127
Accumulated depreciation	$ 11,995
Depreciation life	35 years
Rentable square feet | ft²	140,591
Office Building [Member] | 12790 El Camino Real, Del Mar, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 10,252
Initial cost, buildings and Improvements	21,236
Costs capitalized subsequent to acquisition/ improvement	1,426
Land and improvements, gross	10,252
Buildings and improvements, gross	22,662
Land and improvements and buildings and improvements, gross	32,914
Accumulated depreciation	$ 4,794
Depreciation life	35 years
Rentable square feet | ft²	78,836
Office Building [Member] | 13280 Evening Creek Dr. South, I-15 Corridor, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 3,701
Initial cost, buildings and Improvements	8,398
Costs capitalized subsequent to acquisition/ improvement	4,730
Land and improvements, gross	3,701
Buildings and improvements, gross	13,128
Land and improvements and buildings and improvements, gross	16,829
Accumulated depreciation	$ 5,167
Depreciation life	35 years
Rentable square feet | ft²	41,196
Office Building [Member] | 13290 Evening Creek Dr. South, I-15 Corridor, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 5,229
Initial cost, buildings and Improvements	11,871
Costs capitalized subsequent to acquisition/ improvement	5,919
Land and improvements, gross	5,229
Buildings and improvements, gross	17,790
Land and improvements and buildings and improvements, gross	23,019
Accumulated depreciation	$ 5,950
Depreciation life	35 years
Rentable square feet | ft²	61,180
Office Building [Member] | 13480 Evening Creek Dr. North, I-15 Corridor, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 7,997
Initial cost, buildings and Improvements	0
Costs capitalized subsequent to acquisition/ improvement	52,143
Land and improvements, gross	7,997
Buildings and improvements, gross	52,143
Land and improvements and buildings and improvements, gross	60,140
Accumulated depreciation	$ 18,660
Depreciation life	35 years
Rentable square feet | ft²	154,157
Office Building [Member] | 13500 Evening Creek Dr. North, I-15 Corridor, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 7,581
Initial cost, buildings and Improvements	35,903
Costs capitalized subsequent to acquisition/ improvement	15,331
Land and improvements, gross	7,580
Buildings and improvements, gross	51,235
Land and improvements and buildings and improvements, gross	58,815
Accumulated depreciation	$ 20,471
Depreciation life	35 years
Rentable square feet | ft²	137,658
Office Building [Member] | 13520 Evening Creek Dr. North, I-15 Corridor, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 7,581
Initial cost, buildings and Improvements	35,903
Costs capitalized subsequent to acquisition/ improvement	15,427
Land and improvements, gross	7,580
Buildings and improvements, gross	51,331
Land and improvements and buildings and improvements, gross	58,911
Accumulated depreciation	$ 22,819
Depreciation life	35 years
Rentable square feet | ft²	146,701
Office Building [Member] | 2305 Historic Decatur Rd., Point Loma, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 5,240
Initial cost, buildings and Improvements	22,220
Costs capitalized subsequent to acquisition/ improvement	7,309
Land and improvements, gross	5,240
Buildings and improvements, gross	29,529
Land and improvements and buildings and improvements, gross	34,769
Accumulated depreciation	$ 9,248
Depreciation life	35 years
Rentable square feet | ft²	107,456
Office Building [Member] | 4690 Executive Dr., University Towne Centre, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 1,623
Initial cost, buildings and Improvements	7,926
Costs capitalized subsequent to acquisition/ improvement	3,668
Land and improvements, gross	1,623
Buildings and improvements, gross	11,594
Land and improvements and buildings and improvements, gross	13,217
Accumulated depreciation	$ 7,324
Depreciation life	35 years
Rentable square feet | ft²	47,846
Office Building [Member] | 4100 Bohannon Dr., Menlo Park, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 4,835
Initial cost, buildings and Improvements	15,526
Costs capitalized subsequent to acquisition/ improvement	525
Land and improvements, gross	4,860
Buildings and improvements, gross	16,026
Land and improvements and buildings and improvements, gross	20,886
Accumulated depreciation	$ 3,954
Depreciation life	35 years
Rentable square feet | ft²	47,379
Office Building [Member] | 4200 Bohannon Dr., Menlo Park, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 4,798
Initial cost, buildings and Improvements	15,406
Costs capitalized subsequent to acquisition/ improvement	3,222
Land and improvements, gross	4,662
Buildings and improvements, gross	18,764
Land and improvements and buildings and improvements, gross	23,426
Accumulated depreciation	$ 4,915
Depreciation life	35 years
Rentable square feet | ft²	45,451
Office Building [Member] | 4300 Bohannon Dr., Menlo Park, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 6,527
Initial cost, buildings and Improvements	20,958
Costs capitalized subsequent to acquisition/ improvement	2,955
Land and improvements, gross	6,470
Buildings and improvements, gross	23,970
Land and improvements and buildings and improvements, gross	30,440
Accumulated depreciation	$ 6,996
Depreciation life	35 years
Rentable square feet | ft²	63,079
Office Building [Member] | 4400 Bohannon Dr., Menlo Park, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 4,798
Initial cost, buildings and Improvements	15,406
Costs capitalized subsequent to acquisition/ improvement	2,943
Land and improvements, gross	4,939
Buildings and improvements, gross	18,208
Land and improvements and buildings and improvements, gross	23,147
Accumulated depreciation	$ 5,066
Depreciation life	35 years
Rentable square feet | ft²	48,146
Office Building [Member] | 4500 Bohannon Dr., Menlo Park, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 6,527
Initial cost, buildings and Improvements	20,957
Costs capitalized subsequent to acquisition/ improvement	2,025
Land and improvements, gross	6,470
Buildings and improvements, gross	23,039
Land and improvements and buildings and improvements, gross	29,509
Accumulated depreciation	$ 5,665
Depreciation life	35 years
Rentable square feet | ft²	63,078
Office Building [Member] | 4600 Bohannon Dr., Menlo Park, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 4,798
Initial cost, buildings and Improvements	15,406
Costs capitalized subsequent to acquisition/ improvement	3,326
Land and improvements, gross	4,939
Buildings and improvements, gross	18,591
Land and improvements and buildings and improvements, gross	23,530
Accumulated depreciation	$ 4,924
Depreciation life	35 years
Rentable square feet | ft²	48,147
Office Building [Member] | 4700 Bohannon Dr., Menlo Park, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 6,527
Initial cost, buildings and Improvements	20,958
Costs capitalized subsequent to acquisition/ improvement	1,422
Land and improvements, gross	6,470
Buildings and improvements, gross	22,437
Land and improvements and buildings and improvements, gross	28,907
Accumulated depreciation	$ 5,492
Depreciation life	35 years
Rentable square feet | ft²	63,078
Office Building [Member] | 1290 - 1300 Terra Bella Ave., Mountain View, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 28,730
Initial cost, buildings and Improvements	27,555
Costs capitalized subsequent to acquisition/ improvement	29
Land and improvements, gross	28,730
Buildings and improvements, gross	27,584
Land and improvements and buildings and improvements, gross	56,314
Accumulated depreciation	$ 3,589
Depreciation life	35 years
Rentable square feet | ft²	114,175
Office Building [Member] | 331 Fairchild Dr., Mountain View, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 18,396
Initial cost, buildings and Improvements	17,712
Costs capitalized subsequent to acquisition/ improvement	7,955
Land and improvements, gross	18,396
Buildings and improvements, gross	25,667
Land and improvements and buildings and improvements, gross	44,063
Accumulated depreciation	$ 4,674
Depreciation life	35 years
Rentable square feet | ft²	87,147
Office Building [Member] | 680 E. Middlefield Rd., Mountain View, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 34,605
Initial cost, buildings and Improvements	0
Costs capitalized subsequent to acquisition/ improvement	56,464
Land and improvements, gross	34,605
Buildings and improvements, gross	56,464
Land and improvements and buildings and improvements, gross	91,069
Accumulated depreciation	$ 7,908
Depreciation life	35 years
Rentable square feet | ft²	170,090
Office Building [Member] | 690 E. Middlefield Rd., Mountain View, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 34,755
Initial cost, buildings and Improvements	0
Costs capitalized subsequent to acquisition/ improvement	56,707
Land and improvements, gross	34,755
Buildings and improvements, gross	56,707
Land and improvements and buildings and improvements, gross	91,462
Accumulated depreciation	$ 7,942
Depreciation life	35 years
Rentable square feet | ft²	170,823
Office Building [Member] | 1701 Page Mill Rd, Palo Alto, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 0
Initial cost, buildings and Improvements	99,522
Costs capitalized subsequent to acquisition/ improvement	25
Land and improvements, gross	0
Buildings and improvements, gross	99,547
Land and improvements and buildings and improvements, gross	99,547
Accumulated depreciation	$ 6,000
Depreciation life	35 years
Rentable square feet | ft²	128,688
Office Building [Member] | 3150 Porter Drive, Palo Alto, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 0
Initial cost, buildings and Improvements	21,715
Costs capitalized subsequent to acquisition/ improvement	4
Land and improvements, gross	0
Buildings and improvements, gross	21,719
Land and improvements and buildings and improvements, gross	21,719
Accumulated depreciation	$ 1,591
Depreciation life	35 years
Rentable square feet | ft²	36,897
Office Building [Member] | 900 Jefferson Ave., Redwood City, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 16,668
Initial cost, buildings and Improvements	0
Costs capitalized subsequent to acquisition/ improvement	109,313
Land and improvements, gross	18,063
Buildings and improvements, gross	107,918
Land and improvements and buildings and improvements, gross	125,981
Accumulated depreciation	$ 11,977
Depreciation life	35 years
Rentable square feet | ft²	228,505
Office Building [Member] | 900 Middlefield Rd., Redwood City, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 7,959
Initial cost, buildings and Improvements	0
Costs capitalized subsequent to acquisition/ improvement	49,862
Land and improvements, gross	8,626
Buildings and improvements, gross	49,195
Land and improvements and buildings and improvements, gross	57,821
Accumulated depreciation	$ 5,204
Depreciation life	35 years
Rentable square feet | ft²	118,764
Office Building [Member] | 303 Second St., San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 63,550
Initial cost, buildings and Improvements	154,153
Costs capitalized subsequent to acquisition/ improvement	70,133
Land and improvements, gross	63,550
Buildings and improvements, gross	224,286
Land and improvements and buildings and improvements, gross	287,836
Accumulated depreciation	$ 71,553
Depreciation life	35 years
Rentable square feet | ft²	740,047
Office Building [Member] | 100 First St., San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 49,150
Initial cost, buildings and Improvements	131,238
Costs capitalized subsequent to acquisition/ improvement	63,503
Land and improvements, gross	49,150
Buildings and improvements, gross	194,741
Land and improvements and buildings and improvements, gross	243,891
Accumulated depreciation	$ 53,081
Depreciation life	35 years
Rentable square feet | ft²	467,095
Office Building [Member] | 250 Brannan St., San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 7,630
Initial cost, buildings and Improvements	22,770
Costs capitalized subsequent to acquisition/ improvement	4,466
Land and improvements, gross	7,630
Buildings and improvements, gross	27,236
Land and improvements and buildings and improvements, gross	34,866
Accumulated depreciation	$ 9,786
Depreciation life	35 years
Rentable square feet | ft²	100,850
Office Building [Member] | 201 Third St., San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 19,260
Initial cost, buildings and Improvements	84,018
Costs capitalized subsequent to acquisition/ improvement	66,543
Land and improvements, gross	19,260
Buildings and improvements, gross	150,561
Land and improvements and buildings and improvements, gross	169,821
Accumulated depreciation	$ 46,541
Depreciation life	35 years
Rentable square feet | ft²	346,538
Office Building [Member] | 301 Brannan St., San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 5,910
Initial cost, buildings and Improvements	22,450
Costs capitalized subsequent to acquisition/ improvement	5,109
Land and improvements, gross	5,910
Buildings and improvements, gross	27,559
Land and improvements and buildings and improvements, gross	33,469
Accumulated depreciation	$ 8,375
Depreciation life	35 years
Rentable square feet | ft²	82,834
Office Building [Member] | 360 Third St., San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 0
Initial cost, buildings and Improvements	88,235
Costs capitalized subsequent to acquisition/ improvement	112,885
Land and improvements, gross	28,504
Buildings and improvements, gross	172,616
Land and improvements and buildings and improvements, gross	201,120
Accumulated depreciation	$ 39,931
Depreciation life	35 years
Rentable square feet | ft²	429,796
Office Building [Member] | 333 Brannan St., San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 18,645
Initial cost, buildings and Improvements	0
Costs capitalized subsequent to acquisition/ improvement	78,426
Land and improvements, gross	18,645
Buildings and improvements, gross	78,426
Land and improvements and buildings and improvements, gross	97,071
Accumulated depreciation	$ 6,451
Depreciation life	35 years
Rentable square feet | ft²	185,602
Office Building [Member] | 350 Mission Street, San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 52,815
Initial cost, buildings and Improvements	0
Costs capitalized subsequent to acquisition/ improvement	213,459
Land and improvements, gross	52,815
Buildings and improvements, gross	213,459
Land and improvements and buildings and improvements, gross	266,274
Accumulated depreciation	$ 17,818
Depreciation life	35 years
Rentable square feet | ft²	455,340
Office Building [Member] | 100 Hooper Street, San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 78,564
Initial cost, buildings and Improvements	0
Costs capitalized subsequent to acquisition/ improvement	179,739
Land and improvements, gross	78,564
Buildings and improvements, gross	179,739
Land and improvements and buildings and improvements, gross	258,303
Accumulated depreciation	$ 1,043
Depreciation life	35 years
Office Building [Member] | 345 Brannan St., San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 29,405
Initial cost, buildings and Improvements	113,179
Costs capitalized subsequent to acquisition/ improvement	0
Land and improvements, gross	29,405
Buildings and improvements, gross	113,179
Land and improvements and buildings and improvements, gross	142,584
Accumulated depreciation	$ 0
Depreciation life	35 years
Rentable square feet | ft²	110,030
Office Building [Member] | 345 Oyster Point Blvd., South San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 13,745
Initial cost, buildings and Improvements	18,575
Costs capitalized subsequent to acquisition/ improvement	2
Land and improvements, gross	13,745
Buildings and improvements, gross	18,577
Land and improvements and buildings and improvements, gross	32,322
Accumulated depreciation	$ 611
Depreciation life	35 years
Rentable square feet | ft²	40,410
Office Building [Member] | 347 Oyster Point Blvd, South San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 14,071
Initial cost, buildings and Improvements	18,289
Costs capitalized subsequent to acquisition/ improvement	8
Land and improvements, gross	14,071
Buildings and improvements, gross	18,297
Land and improvements and buildings and improvements, gross	32,368
Accumulated depreciation	$ 602
Depreciation life	35 years
Rentable square feet | ft²	39,780
Office Building [Member] | 349 Oyster Point Blvd., South San Francisco, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 23,112
Initial cost, buildings and Improvements	22,601
Costs capitalized subsequent to acquisition/ improvement	771
Land and improvements, gross	23,112
Buildings and improvements, gross	23,372
Land and improvements and buildings and improvements, gross	46,484
Accumulated depreciation	$ 919
Depreciation life	35 years
Rentable square feet | ft²	65,340
Office Building [Member] | 505 Mathilda Ave., Sunnyvale, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 37,843
Initial cost, buildings and Improvements	1,163
Costs capitalized subsequent to acquisition/ improvement	50,450
Land and improvements, gross	37,943
Buildings and improvements, gross	51,513
Land and improvements and buildings and improvements, gross	89,456
Accumulated depreciation	$ 6,388
Depreciation life	35 years
Rentable square feet | ft²	212,322
Office Building [Member] | 555 Mathilda Ave., Sunnyvale, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 37,843
Initial cost, buildings and Improvements	1,163
Costs capitalized subsequent to acquisition/ improvement	50,447
Land and improvements, gross	37,943
Buildings and improvements, gross	51,510
Land and improvements and buildings and improvements, gross	89,453
Accumulated depreciation	$ 6,387
Depreciation life	35 years
Rentable square feet | ft²	212,322
Office Building [Member] | 605 Mathilda Ave., Sunnyvale, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 29,014
Initial cost, buildings and Improvements	891
Costs capitalized subsequent to acquisition/ improvement	77,281
Land and improvements, gross	29,090
Buildings and improvements, gross	78,096
Land and improvements and buildings and improvements, gross	107,186
Accumulated depreciation	$ 14,036
Depreciation life	35 years
Rentable square feet | ft²	162,785
Office Building [Member] | 599 Mathilda Ave., Sunnyvale, CA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 13,538
Initial cost, buildings and Improvements	12,559
Costs capitalized subsequent to acquisition/ improvement	58
Land and improvements, gross	13,538
Buildings and improvements, gross	12,617
Land and improvements and buildings and improvements, gross	26,155
Accumulated depreciation	$ 3,568
Depreciation life	35 years
Rentable square feet | ft²	76,031
Office Building [Member] | 601 108th Ave., Bellevue, WA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 0
Initial cost, buildings and Improvements	214,095
Costs capitalized subsequent to acquisition/ improvement	33,860
Land and improvements, gross	0
Buildings and improvements, gross	247,955
Land and improvements and buildings and improvements, gross	247,955
Accumulated depreciation	$ 70,018
Depreciation life	35 years
Rentable square feet | ft²	488,470
Office Building [Member] | 10900 NE 4th St., Bellevue, WA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 25,080
Initial cost, buildings and Improvements	150,877
Costs capitalized subsequent to acquisition/ improvement	36,619
Land and improvements, gross	25,080
Buildings and improvements, gross	187,496
Land and improvements and buildings and improvements, gross	212,576
Accumulated depreciation	$ 46,105
Depreciation life	35 years
Rentable square feet | ft²	428,557
Office Building [Member] | 837 N. 34th St., Lake Union, WA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 0
Initial cost, buildings and Improvements	37,404
Costs capitalized subsequent to acquisition/ improvement	3,817
Land and improvements, gross	0
Buildings and improvements, gross	41,221
Land and improvements and buildings and improvements, gross	41,221
Accumulated depreciation	$ 9,697
Depreciation life	35 years
Rentable square feet | ft²	111,580
Office Building [Member] | 701 N. 34th St., Lake Union, WA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 0
Initial cost, buildings and Improvements	48,027
Costs capitalized subsequent to acquisition/ improvement	7,989
Land and improvements, gross	0
Buildings and improvements, gross	56,016
Land and improvements and buildings and improvements, gross	56,016
Accumulated depreciation	$ 13,785
Depreciation life	35 years
Rentable square feet | ft²	138,994
Office Building [Member] | 801 N. 34th St., Lake Union, WA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 0
Initial cost, buildings and Improvements	58,537
Costs capitalized subsequent to acquisition/ improvement	1,657
Land and improvements, gross	0
Buildings and improvements, gross	60,194
Land and improvements and buildings and improvements, gross	60,194
Accumulated depreciation	$ 14,159
Depreciation life	35 years
Rentable square feet | ft²	169,412
Office Building [Member] | 320 Westlake Avenue North, WA[Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, encumbrances	$ 74,479
Initial cost, land and improvements	14,710
Initial cost, buildings and Improvements	82,018
Costs capitalized subsequent to acquisition/ improvement	5,063
Land and improvements, gross	14,710
Buildings and improvements, gross	87,081
Land and improvements and buildings and improvements, gross	101,791
Accumulated depreciation	$ 16,693
Depreciation life	35 years
Rentable square feet | ft²	184,644
Office Building [Member] | 321 Terry Avenue North, Lake Union, WA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 10,430
Initial cost, buildings and Improvements	60,003
Costs capitalized subsequent to acquisition/ improvement	9,987
Land and improvements, gross	10,430
Buildings and improvements, gross	69,990
Land and improvements and buildings and improvements, gross	80,420
Accumulated depreciation	$ 13,046
Depreciation life	35 years
Rentable square feet | ft²	135,755
Office Building [Member] | 401 Terry Avenue North, Lake Union, WA [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, land and improvements	$ 22,500
Initial cost, buildings and Improvements	77,046
Costs capitalized subsequent to acquisition/ improvement	0
Land and improvements, gross	22,500
Buildings and improvements, gross	77,046
Land and improvements and buildings and improvements, gross	99,546
Accumulated depreciation	$ 12,888
Depreciation life	35 years
Rentable square feet | ft²	140,605
Undeveloped Land and CIP Properties [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, encumbrances	$ 0
Initial cost, land and improvements	940,092
Initial cost, buildings and Improvements	0
Costs capitalized subsequent to acquisition/ improvement	1,118,418
Land and improvements, gross	940,092
Buildings and improvements, gross	1,118,418
Land and improvements and buildings and improvements, gross	2,058,510
Accumulated depreciation	$ 0
Rentable square feet | ft²	0

Schedule III - Real Estate an_3

Schedule III - Real Estate and Accumulated Depreciation - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)ft²property_units	Dec. 31, 2017USD ($)
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, encumbrances	$ 335,811
Rentable square feet | ft²	13,232,580
Debt premium	$ 800
Aggregate cost of property for federal income tax purposes	7,000,000
Aggregate cost of property held in a VIE	$ 100,000
Building [Member]
Real Estate and Accumulated Depreciation [Line Items]
Depreciation life	35 years
Tenant Improvements [Member] | Minimum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property depreciable lives	1 year
Tenant Improvements [Member] | Maximum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property depreciable lives	20 years
Office Building [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial cost, encumbrances	$ 335,811
Rentable square feet | ft²	13,232,580
1550 N. El Centro Avenue, Los Angeles, CA [Member] | Office Building [Member]
Real Estate and Accumulated Depreciation [Line Items]
Depreciation life	35 years
Number of building units | property_units	200
12100 W. Olympic Blvd., Los Angeles, CA [Member] | Office Building [Member]
Real Estate and Accumulated Depreciation [Line Items]
Depreciation life	35 years
Initial cost, encumbrances	$ 170,000
Rentable square feet | ft²	152,048
2100/2110 Colorado Ave., Santa Monica, CA [Member] | Office Building [Member]
Real Estate and Accumulated Depreciation [Line Items]
Depreciation life	35 years
Initial cost, encumbrances	$ 91,332
Rentable square feet | ft²	102,864
320 Westlake Avenue North, WA[Member] | Office Building [Member]
Real Estate and Accumulated Depreciation [Line Items]
Depreciation life	35 years
Initial cost, encumbrances	$ 74,479
Rentable square feet | ft²	184,644
100 Hooper Street, San Francisco, CA [Member] | Office Building [Member]
Real Estate and Accumulated Depreciation [Line Items]
Depreciation life	35 years
Kilroy Realty L.P. [Member]
Real Estate and Accumulated Depreciation [Line Items]
Unamortized debt issuance expense	$ 17,400
Kilroy Realty L.P. [Member] | Secured debt [Member]
Real Estate and Accumulated Depreciation [Line Items]
Debt premium	800
Unamortized debt issuance expense	$ 1,039	$ 1,175
Development Projects in Lease-Up [Member] | 100 Hooper Street, San Francisco, CA [Member] | Office Building [Member]
Real Estate and Accumulated Depreciation [Line Items]
Rentable square feet | ft²	400,000

Schedule III - Real Estate an_4

Schedule III - Real Estate and Accumulated Depreciation - Historical Cost Real Estate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate [Roll Forward]
Total real estate held for investment, beginning of year	$ 7,417,777	$ 7,060,754	$ 6,328,146
Acquisitions	581,671	19,829	460,957
Improvements, etc.	991,008	533,939	386,836
Total additions during period	1,572,679	553,768	847,793
Cost of real estate sold	(286,623)	(191,610)	(68,200)
Properties held for sale	0	0	(13,193)
Other	(277,201)	(5,135)	(33,792)
Total deductions during period	(563,824)	(196,745)	(115,185)
Total real estate held for investment, end of year	$ 8,426,632	$ 7,417,777	$ 7,060,754

Schedule III - Real Estate an_5

Schedule III - Real Estate and Accumulated Depreciation - Accumulated Depreciation Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation [Roll Forward]
Accumulated depreciation, beginning of year	$ 1,264,162	$ 1,139,853	$ 994,241
Depreciation of real estate	198,578	190,515	171,983
Total additions during period	198,578	190,515	171,983
Write-offs due to sale	(71,372)	(66,206)	(22,471)
Properties held for sale	0	0	(3,900)
Other	0	0	0
Total deductions during period	(71,372)	(66,206)	(26,371)
Accumulated depreciation, end of year	$ 1,391,368	$ 1,264,162	$ 1,139,853