Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
ASSETS
Real estate, at cost	$ 13,165,836	$ 12,303,965
Construction in progress	937,475	818,685
Land held for future development	273,922	266,822
Less: accumulated depreciation	(2,843,167)	(2,642,986)
Total real estate	11,534,066	10,746,486
Cash and cash equivalents	1,223,215	1,823,208
Cash held in escrows	32,253	40,332
Investments in securities	11,792	9,548
Tenant and other receivables (net of allowance for doubtful accounts of $1,381 and $1,766, respectively)	45,039	79,838
Related party notes receivable	282,206	280,442
Interest receivable from related party notes receivable	102,122	89,854
Accrued rental income (net of allowance of $2,771 and $2,515, respectively)	579,553	522,675
Deferred charges, net	534,898	445,403
Prepaid expenses and other assets	132,109	75,458
Investments in unconsolidated joint ventures	664,690	669,722
Total assets	15,141,943	14,782,966
Liabilities:
Mortgage notes payable	2,848,686	3,123,267
Unsecured senior notes (net of discount of $10,783 and $9,814, respectively)	4,639,217	3,865,186
Unsecured exchangeable senior notes (net of discount of $2,012 and $3,462, respectively)	1,162,955	1,715,685
Unsecured line of credit
Accounts payable and accrued expenses	193,492	155,139
Dividends and distributions payable	93,461	91,901
Accrued interest payable	98,601	69,105
Other liabilities	309,004	293,515
Total liabilities	9,345,416	9,313,798
Commitments and contingencies
Noncontrolling interest:
Redeemable preferred units of the Operating Partnership	110,876	55,652
Equity:
Excess stock, $.01 par value, 150,000,000 shares authorized, none issued or outstanding
Preferred stock, $.01 par value, 50,000,000 shares authorized, none issued or outstanding
Common stock, $.01 par value, 250,000,000 shares authorized, 150,935,137 and 148,186,511 issued and 150,856,237 and 148,107,611 outstanding at September 30, 2012 and December 31, 2011, respectively	1,509	1,481
Additional paid-in capital	5,194,569	4,936,457
Dividends in excess of earnings	(59,621)	(53,080)
Treasury common stock at cost, 78,900 shares at September 30, 2012 and December 31, 2011	(2,722)	(2,722)
Accumulated other comprehensive loss	(14,379)	(16,138)
Total stockholders' equity attributable to Boston Properties, Inc.	5,119,356	4,865,998
Noncontrolling interests:
Common units of the Operating Partnership	568,147	548,581
Property partnerships	(1,852)	(1,063)
Total equity	5,685,651	5,413,516
Total liabilities and equity	$ 15,141,943	$ 14,782,966