Co-investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	$ 964,970		$ 964,970		$ 677,133
Balance sheets [Abstract]
Rental properties and real estate under development	422,372		422,372		50,430
Other liabilities	32,896		32,896		24,871
Statement of operations [Abstract]
Interest expense	(42,151)	(29,327)	(71,192)	(57,468)
General and administrative	(9,558)	(6,589)	(17,142)	(13,588)
Equity income in co-investments	5,629	7,282	16,155	11,493
Ownership interest (in hundredths)	50.00%		50.00%
Membership interest in Wesco I [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	136,100		136,100		142,025
Membership interest in Wesco III [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	54,059		54,059		39,073
Partnership interest in Fund II [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	2,484		2,484		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	11,561		11,561		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	11,585		11,585		11,224
Membership interest in Wesco IV [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	97,840		97,840		0
Balance sheets [Abstract]
Company's share of equity	297,700		297,700
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	94,958		94,958		0
Balance sheets [Abstract]
Company's share of equity	516,100		516,100
Statement of operations [Abstract]
Ownership interest (in hundredths)	50.00%		50.00%
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	408,587		408,587		208,529
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	372,477		372,477		301,538
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	8,155		8,155		7,321
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	30,942		30,942		17,115
Total development co-investments [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	411,574		411,574		325,974
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	95,527		95,527		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	16,135		16,135		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	9,913		9,913		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	9,410		9,410		8,865
Preferred return rate (in hundredths)			12.00%
Total preferred interest investments [Member]
Investments in joint ventures accounted for under the equity method of accounting [Abstract]
Total co-investment	144,809		144,809		142,630
Total co investment [Member]
Balance sheets [Abstract]
Rental properties and real estate under development	2,980,972		2,980,972		1,953,328
Other assets	113,794		113,794		61,578
Total assets	3,094,766		3,094,766		2,014,906
Debt	1,248,579		1,248,579		667,641
Other liabilities	83,310		83,310		125,479
Equity	1,762,877		1,762,877		1,221,786
Total liabilities and equity	3,094,766		3,094,766		2,014,906
Company's share of equity	964,970		964,970		677,133
Statement of operations [Abstract]
Property revenues	48,784	26,258	76,744	54,117
Property operating expenses	(18,556)	(9,874)	(30,116)	(19,702)
Net property operating income	30,228	16,384	46,628	34,415
Gain on sale of real estate	0	8,817	11,369	8,817
Interest expense	(9,422)	(6,094)	(15,445)	(12,872)
General and administrative	(1,811)	(1,539)	(3,199)	(3,053)
Equity income in co-investments	4,784	4,657	9,543	9,279
Depreciation and Amortization	(17,885)	(9,577)	(28,578)	(20,596)
Net income	5,894	12,648	20,318	15,990
Company's share of net income	$ 5,629	$ 7,282	$ 16,155	$ 11,493