18. Supplemental Consolidating Financial Data for Subsidiary Guarantors of the Unsecured Notes Supplemental Consolidating Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Land	$ 105,890		$ 94,203
Buildings and improvements	3,018,361		2,736,936
Income producing property	3,124,251		2,831,139
Less: accumulated depreciation	(662,183)		(560,837)
Net income producing property	2,462,068		2,270,302
Construction in progress and land held for development	330,983	[1]	300,939
Net real estate	2,793,051		2,571,241
Cash and cash equivalents	38,624		31,230	$ 29,598	$ 38,733
Rents and other receivables	11,533		9,588
Deferred rent, net	123,058		128,941
Lease contracts above market value, net	5,138		6,029
Deferred costs, net	25,776		23,774
Prepaid expenses and other assets	41,284		44,689
Total assets	3,038,464		2,815,492
Unsecured Credit Facility	50,926		0
Mortgage notes payable	110,733		114,075
Unsecured Term Loan	249,036		249,172
Unsecured notes payable	837,323		834,963
Accounts payable and accrued liabilities	36,909		32,301
Construction costs payable	56,428		22,043
Accrued interest payable	11,592		11,821
Distribution payable	46,352		43,906
Lease contracts below market value, net	2,830		4,132
Prepaid rents and other liabilities	78,232		67,477
Total liabilities	1,480,361		1,379,890
Redeemable noncontrolling interests - operating partnership	591,101		479,189
Commitments and contingencies	0		0
Total liabilities and stockholders’ equity	3,038,464		2,815,492
Subsidiaries [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Land	105,890		94,203
Buildings and improvements	3,018,361		2,736,936
Income producing property	3,124,251		2,831,139
Less: accumulated depreciation	(662,183)		(560,837)
Net income producing property	2,462,068		2,270,302
Construction in progress and land held for development	330,983		300,939
Net real estate	2,793,051		2,571,241
Cash and cash equivalents	34,409		27,015	25,380	34,514
Rents and other receivables	11,533		9,588
Deferred rent, net	123,058		128,941
Lease contracts above market value, net	5,138		6,029
Deferred costs, net	25,776		23,774
Investment in affiliates	0		0
Prepaid expenses and other assets	41,284		44,689
Total assets	3,034,249		2,811,277
Unsecured Credit Facility	50,926		0
Mortgage notes payable	110,733		114,075
Unsecured Term Loan	249,036		249,172
Unsecured notes payable	837,323		834,963
Accounts payable and accrued liabilities	36,909		32,301
Construction costs payable	56,428		22,043
Accrued interest payable	11,592		11,821
Distribution payable	46,352		43,906
Lease contracts below market value, net	2,830		4,132
Prepaid rents and other liabilities	78,232		67,477
Total liabilities	1,480,361		1,379,890
Redeemable noncontrolling interests - operating partnership	591,101		479,189
Commitments and contingencies	0		0
Limited Partners' Capital	201,250
General Partners' Capital	6,645		6,021
Total partners’ capital	962,787		952,198	1,111,123	1,248,055
Total liabilities and stockholders’ equity	3,034,249		2,811,277
Subsidiaries [Member] | Operating Partnership [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Land	0		0
Buildings and improvements	0		0
Income producing property	0		0
Less: accumulated depreciation	0		0
Net income producing property	0		0
Construction in progress and land held for development	0		0
Net real estate	0		0
Cash and cash equivalents	31,781		21,697	21,806	32,903
Rents and other receivables	1,390		1,391
Deferred rent, net	0		0
Lease contracts above market value, net	0		0
Deferred costs, net	6,066		3,236
Investment in affiliates	2,713,096		2,546,465
Prepaid expenses and other assets	3,463		3,025
Total assets	2,755,796		2,575,814
Unsecured Credit Facility	50,926		0
Mortgage notes payable	0		0
Unsecured Term Loan	249,036		249,172
Unsecured notes payable	837,323		834,963
Accounts payable and accrued liabilities	6,477		4,516
Construction costs payable	0		43
Accrued interest payable	11,578		11,815
Distribution payable	46,352		43,906
Lease contracts below market value, net	0		0
Prepaid rents and other liabilities	216		12
Total liabilities	1,201,908		1,144,427
Redeemable noncontrolling interests - operating partnership	591,101		479,189
Commitments and contingencies	0		0
General Partners' Capital	6,645		6,021
Total partners’ capital	962,787		952,198
Total liabilities and stockholders’ equity	2,755,796		2,575,814
Subsidiaries [Member] | Subsidiary Guarantors [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Land	80,673		84,258
Buildings and improvements	2,332,771		2,399,016
Income producing property	2,413,444		2,483,274
Less: accumulated depreciation	(605,488)		(522,096)
Net income producing property	1,807,956		1,961,178
Construction in progress and land held for development	88,836		25,545
Net real estate	1,896,792		1,986,723
Cash and cash equivalents	0		0	0	0
Rents and other receivables	4,743		7,563
Deferred rent, net	109,142		122,830
Lease contracts above market value, net	5,138		6,029
Deferred costs, net	11,632		14,250
Investment in affiliates	0		0
Prepaid expenses and other assets	27,341		39,642
Total assets	2,054,788		2,177,037
Unsecured Credit Facility	0		0
Mortgage notes payable	0		0
Unsecured Term Loan	0		0
Unsecured notes payable	0		0
Accounts payable and accrued liabilities	22,319		23,615
Construction costs payable	10,159		293
Accrued interest payable	0		0
Distribution payable	0		0
Lease contracts below market value, net	2,830		4,132
Prepaid rents and other liabilities	58,599		62,630
Total liabilities	93,907		90,670
Redeemable noncontrolling interests - operating partnership	0		0
Commitments and contingencies	0		0
General Partners' Capital	0		0
Total partners’ capital	1,960,881		2,086,367
Total liabilities and stockholders’ equity	2,054,788		2,177,037
Subsidiaries [Member] | Subsidiary Non-Guarantors [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Land	25,217		9,945
Buildings and improvements	685,590		337,920
Income producing property	710,807		347,865
Less: accumulated depreciation	(56,695)		(38,741)
Net income producing property	654,112		309,124
Construction in progress and land held for development	242,147		275,394
Net real estate	896,259		584,518
Cash and cash equivalents	2,628		5,318	3,574	1,611
Rents and other receivables	5,400		634
Deferred rent, net	13,916		6,111
Lease contracts above market value, net	0		0
Deferred costs, net	8,078		6,288
Investment in affiliates	0		0
Prepaid expenses and other assets	10,480		2,022
Total assets	936,761		604,891
Unsecured Credit Facility	0		0
Mortgage notes payable	110,733		114,075
Unsecured Term Loan	0		0
Unsecured notes payable	0		0
Accounts payable and accrued liabilities	8,113		4,170
Construction costs payable	46,269		21,707
Accrued interest payable	14		6
Distribution payable	0		0
Lease contracts below market value, net	0		0
Prepaid rents and other liabilities	19,417		4,835
Total liabilities	184,546		144,793
Redeemable noncontrolling interests - operating partnership	0		0
Commitments and contingencies	0		0
General Partners' Capital	0		0
Total partners’ capital	752,215		460,098
Total liabilities and stockholders’ equity	936,761		604,891
Subsidiaries [Member] | Eliminations [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Land	0		0
Buildings and improvements	0		0
Income producing property	0		0
Less: accumulated depreciation	0		0
Net income producing property	0		0
Construction in progress and land held for development	0		0
Net real estate	0		0
Cash and cash equivalents	0		0	$ 0	$ 0
Rents and other receivables	0		0
Deferred rent, net	0		0
Lease contracts above market value, net	0		0
Deferred costs, net	0		0
Investment in affiliates	(2,713,096)		(2,546,465)
Prepaid expenses and other assets	0		0
Total assets	(2,713,096)		(2,546,465)
Unsecured Credit Facility	0		0
Mortgage notes payable	0		0
Unsecured Term Loan	0		0
Unsecured notes payable	0		0
Accounts payable and accrued liabilities	0		0
Construction costs payable	0		0
Accrued interest payable	0		0
Distribution payable	0		0
Lease contracts below market value, net	0		0
Prepaid rents and other liabilities	0		0
Total liabilities	0		0
Redeemable noncontrolling interests - operating partnership	0		0
Commitments and contingencies	0		0
General Partners' Capital	0		0
Total partners’ capital	(2,713,096)		(2,546,465)
Total liabilities and stockholders’ equity	(2,713,096)		(2,546,465)
Subsidiaries [Member] | Series A Preferred Stock [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital			185,000
Subsidiaries [Member] | Series A Preferred Stock [Member] | Operating Partnership [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital			185,000
Subsidiaries [Member] | Series A Preferred Stock [Member] | Subsidiary Guarantors [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital			0
Subsidiaries [Member] | Series A Preferred Stock [Member] | Subsidiary Non-Guarantors [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital			0
Subsidiaries [Member] | Series A Preferred Stock [Member] | Eliminations [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital			0
Subsidiaries [Member] | Series B Preferred Stock [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital			166,250
Subsidiaries [Member] | Series B Preferred Stock [Member] | Operating Partnership [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital			166,250
Subsidiaries [Member] | Series B Preferred Stock [Member] | Subsidiary Guarantors [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital			0
Subsidiaries [Member] | Series B Preferred Stock [Member] | Subsidiary Non-Guarantors [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital			0
Subsidiaries [Member] | Series B Preferred Stock [Member] | Eliminations [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital			0
Subsidiaries [Member] | Series C Preferred Stock [Member] | Operating Partnership [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital	201,250
Subsidiaries [Member] | Series C Preferred Stock [Member] | Subsidiary Guarantors [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital	0
Subsidiaries [Member] | Series C Preferred Stock [Member] | Subsidiary Non-Guarantors [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital	0
Subsidiaries [Member] | Series C Preferred Stock [Member] | Eliminations [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital	0
Subsidiaries [Member] | Limited partners' common units [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital	754,892		594,927
Subsidiaries [Member] | Limited partners' common units [Member] | Operating Partnership [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital	754,892		594,927
Subsidiaries [Member] | Limited partners' common units [Member] | Subsidiary Guarantors [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital	1,960,881		2,086,367
Subsidiaries [Member] | Limited partners' common units [Member] | Subsidiary Non-Guarantors [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital	752,215		460,098
Subsidiaries [Member] | Limited partners' common units [Member] | Eliminations [Member]
Supplemental Consolidating Statements Of Balance Sheets [Line Items]
Limited Partners' Capital	$ (2,713,096)		$ (2,546,465)

[1] (1)Properties located in Ashburn, VA (ACC8, ACC9, ACC10, and ACC11), Elk Grove Village, IL (CH3), Santa Clara, CA (SC1 Phase III, formerly referred to as SC2), Hillsboro, OR (OR1 and OR2) and Vaughan, ON (TOR1).