Equity Based Compensation Plans, Restricted stock activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restricted Stock [Member]
Shares [Roll forward]
Unvested at beginning of year (in shares)	54,676	25,820	16,176
Granted (in shares)	49,183	56,177	22,014
Granted - BRE restricted stock converted (in shares)	0	0	119,411
Vested (in shares)	(38,427)	(22,939)	(126,931)
Forfeited and canceled (in shares)	(7,083)	(4,382)	(4,850)
Unvested at end of year (in shares)	58,349	54,676	25,820	16,176
Weighted-average grant price [Abstract]
Unvested at beginning of year (in dollars per share)	$ 147.10	$ 168.22	$ 108.06
Granted (in dollars per share)	150.13	155.21	194.03
Granted - BRE restricted stock converted (in dollars per share)	0.00	0.00	173.82
Vested (in dollars per share)	147.12	148.20	171.56
Forfeited and canceled (in dollars per share)	141.76	122.06	135.10
Unvested at end of year (in dollars per share)	$ 149.11	$ 147.10	$ 168.22	$ 108.06
Long Term Incentive Plans - Z Units and 2014 LTIP Units [Member]
Shares [Roll forward]
Unvested at beginning of year (in shares)	106,157	151,067	149,381
Granted (in shares)	0	0	44,750
Vested (in shares)	36,842	36,650	41,729
Converted (in shares)	0	0	0
Forfeited and canceled (in shares)	(9,288)	(8,260)	(1,335)
Unvested at end of year (in shares)	60,027	106,157	151,067	149,381
Weighted-average grant price [Abstract]
Unvested at beginning of year (in dollars per share)	$ 75.41	$ 71.14	$ 63.53
Unvested at end of year (in dollars per share)	$ 75.11	$ 75.41	$ 71.14	$ 63.53
Incentive units vested [Roll Forward]
Vested, beginning balance (in shares)	144,185	181,919	118,190
Vested, units granted (in shares)	0	0	24,000
Vested, units vested (in shares)	36,842	36,650	41,729
Converted (in shares)	0	(74,384)	(2,000)
Cancelled (in shares)	0	0	0
Vested, ending balance (in shares)	181,027	144,185	181,919	118,190
Total outstanding incentive units [Abstract]
Total outstanding units, beginning balance (in shares)	250,342	332,986	267,571
Total outstanding units, granted (in shares)	0	0	68,750
Total outstanding units, vested (in shares)	0	0	0
Total outstanding units, converted (in shares)	0	(74,384)	(2,000)
Total outstanding units, cancelled (in shares)	(9,288)	(8,260)	(1,335)
Total outstanding units, ending balance (in shares)	241,054	250,342	332,986	267,571
Weighted average remaining contractual life outstanding units	8 years 6 months	9 years 6 months	10 years 6 months	9 years 3 months 18 days