Co-investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013	Nov. 04, 2014	Oct. 31, 2014	Dec. 31, 2013
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	$ 1,043,277			$ 1,043,277					$ 677,133
Balance sheets [Abstract]
Rental properties and real estate under development	363,193			363,193					50,430
Other liabilities	32,330			32,330					24,871
Statement of operations [Abstract]
Interest expense	(45,830)		(29,192)	(117,021)		(86,661)
General and administrative	(11,479)		(6,263)	(28,621)		(19,852)
Equity income in co-investments	4,910		40,802	21,065		52,295
Ownership interest (in hundredths)	50.00%			50.00%			28.20%	50.00%
Membership interest in Wesco I [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	135,875			135,875					142,025
Membership interest in Wesco III [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	53,411			53,411					39,073
Partnership interest in Fund II [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	2,578			2,578					4,166
Membership interest in a limited liability company that owns Expo [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	8,305			8,305					12,041
Membership interest in a limited liability company that owns The Huxley [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	11,784			11,784					11,224
Membership interest in limited liability company that owns Connolly Station [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	47,661			47,661					45,242
Membership interest in Wesco IV [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	95,338			95,338					0
Balance sheets [Abstract]
Company's share of equity	297,800			297,800
Statement of operations [Abstract]
Ownership interest (in hundredths)	50.00%			50.00%
Percentage of pro rata income or loss related to performance incentive (in hundredths)				50.00%
Number of apartment communities	5			5
Number of units	1,116			1,116
Membership interest in Wesco IV [Member] | Minimum [Member]
Statement of operations [Abstract]
Debt usage percentage (in hundredths)	50.00%			50.00%
Membership interest in Wesco IV [Member] | Maximum [Member]
Statement of operations [Abstract]
Debt usage percentage (in hundredths)	60.00%			60.00%
Membership interest in BEXAEW [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	89,504			89,504					0
Balance sheets [Abstract]
Company's share of equity	516,700			516,700
Statement of operations [Abstract]
Ownership interest (in hundredths)	50.00%			50.00%
Number of apartment communities	9			9
Number of units	2,723			2,723
Total operating co-investments [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	444,456			444,456					253,771
Membership interests in limited liability companies with CPPIB that own and are developing Epic, Connolly Station, Mosso I & II, Park 20, and The Village [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	364,779	[1]		364,779	[1]				256,296	[1]
Membership interests in limited liability companies that owns and is developing One South Market [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	30,498			30,498					17,115
Membership interests in limited liability companies that own and are developing The Dylan [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	8,396			8,396					7,321
Membership interests in limited liability companies that own and are developing Century Towers [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	13,491			13,491					0
Total development co-investments [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	417,164			417,164					280,732
Membership interest in Wesco II that owns a preferred equity interest in Park Merced with a preferred return of 10.1% [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	95,934			95,934					94,711
Preferred return rate (in hundredths)				10.10%
Preferred interests in related party limited liability companies that owns Sage at Cupertino with a preferred return of 9.5% [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	16,471			16,471					15,775
Preferred return rate (in hundredths)				9.50%
Preferred interest in a related party limited liability company that owns Madison Park at Anaheim with a preferred return of 9% [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	13,824			13,824					13,824
Preferred return rate (in hundredths)				9.00%
Preferred interest in related party limited liability company that owns an apartment development in Redwood City with a preferred return of 12% [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	10,148			10,148					9,455
Preferred return rate (in hundredths)				12.00%
Preferred interest in a limited liability company that owns an apartment development in San Jose with a preferred return of 12% [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	9,710			9,710					8,865
Preferred return rate (in hundredths)				12.00%
Preferred interest in a limited liability company that owns 8th & Thomas with a preferred return of 10.0% [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	12,816			12,816					0
Preferred return rate (in hundredths)				10.00%
Preferred interest in a limited liability company that owns Newbury Park with a preferred return of 12.0% [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	12,754			12,754					0
Preferred return rate (in hundredths)				12.00%
Preferred interest in a limited liability company that owns Century Towers with a preferred return of 10.0% [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	10,000			10,000					0
Preferred return rate (in hundredths)				10.00%
Total preferred interest investments [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	181,657			181,657					142,630
Total co investment [Member]
Balance sheets [Abstract]
Rental properties and real estate under development	3,084,852			3,084,852					1,953,328
Other assets	110,752			110,752					61,578
Total assets	3,195,604			3,195,604					2,014,906
Debt	1,285,954			1,285,954					667,641
Other liabilities	83,344			83,344					125,479
Equity	1,826,306			1,826,306					1,221,786
Total liabilities and equity	3,195,604			3,195,604					2,014,906
Company's share of equity	1,043,277			1,043,277					677,133
Statement of operations [Abstract]
Property revenues	51,725		24,796	128,469		78,913
Property operating expenses	(18,759)		(10,170)	(48,875)		(29,872)
Net property operating income	32,966		14,626	79,594		49,041
Gain on sale of real estate	0		137,845	11,369		146,663
Interest expense	(9,838)		(6,052)	(25,283)		(18,924)
General and administrative	(1,840)		(1,419)	(5,039)		(4,472)
Equity income in co-investments	4,808		0	14,351		0
Depreciation and Amortization	(21,357)		(8,718)	(49,935)		(29,314)
Net income	4,739		136,282	25,057		142,994
Company's share of net income	$ 4,910		$ 40,802	$ 21,065		$ 52,295

[1] Epic Phase I and II are currently in operations. The co-invesment will be moved to operating co-investment with the completion of Phase III.