Equity Based Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2015

Share-based Compensation [Abstract]

Weighted average assumptions used to estimate fair value of stock options

The fair value of stock options was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions used for grants:

	2015			2014			2013
Stock price	$	227.75		$	176.65		$	153.54
Risk-free interest rates	1.83		%	2.37		%	2.68		%
Expected lives	6 years			8 years			8 years
Volatility	20.06		%	18.00		%	18.03		%
Dividend yield	2.73		%	2.90		%	3.15		%

Summary of stock options activity

A summary of the status of the Company’s stock option plans as of December 31, 2015, 2014, and 2013 and changes during the years ended on those dates is presented below:

	2015				2014				2013
	Shares		Weighted- average exercise price		Shares		Weighted- average exercise price		Shares		Weighted- average exercise price
Outstanding at beginning of year	664,785		$	138.78	695,488		$	133.37	623,434		$	125.96
Granted	78,600		227.75		42,518		176.65		150,325		153.54
Granted - BRE options converted	—		—		133,766		121.03		—		—
Exercised	(203,556	)	131.53		(185,387	)	113.72		(52,970	)	102.43
Forfeited and canceled	(14,735	)	136.11		(21,600	)	144.29		(25,301	)	135.25
Outstanding at end of year	525,094		154.98		664,785		138.78		695,488		133.37
Options exercisable at year end	342,048		152.42		395,986		133.99		300,632		119.09

Summary information of stock options outstanding

The following table summarizes information about stock options outstanding as of December 31, 2015:

	Options outstanding				Options exercisable
	Number outstanding as of	Weighted- average remaining	Weighted- average		Number exercisable as of	Weighted- average
Range of	December 31,	contractual	exercise		December 31,	exercise
exercise prices	2015	life (years)	price		2015	price
$66.05 - $101.01	15,901	3.2	$	74.47	15,901	$	74.47
$105.64 - $161.98	367,024	5.3	139.73		218,041	135.00
$164.76 - $229.43	142,169	7.5	203.37		108,106	199.02
	525,094	5.8	154.98		342,048	152.42

Restricted stock activity

The following table summarizes information about restricted stock outstanding as of December 31, 2015, 2014 and 2013 and changes during the years ended:

	2015				2014				2013
	Shares		Weighted- average grant price		Shares		Weighted- average grant price		Shares		Weighted- average grant price
Unvested at beginning of year	25,820		$	168.22	16,176		$	108.06	24,922		$	104.52
Granted	56,177		155.21		22,014		194.03		1,556		158.75
Granted - BRE restricted stock converted	—		—		119,411		173.82		—		—
Vested	(22,939	)	148.20		(126,931	)	171.56		(7,211	)	109.86
Forfeited and canceled	(4,382	)	122.06		(4,850	)	135.10		(3,091	)	100.84
Unvested at end of year	54,676		147.10		25,820		168.22		16,176		108.06

Summary of long term incentive plan - Z Units

The following table summarizes information about the LTIP Units outstanding as of December 31, 2015 ($ in thousands):

	Long Term Incentive Plan - LTIP Units
	Total Vested Units		Total Unvested Units		Total Outstanding Units		Weighted- average Grant-date Fair Value		Weighted- average Remaining Contractual Life (years)
Balance, December 31, 2012	190,704		140,043		330,747		$	58.44	11.3
Granted	—		50,500		50,500
Vested	35,919		(35,919	)	—
Converted	(108,433	)	—		(108,433	)
Cancelled	—		(5,243	)	(5,243	)
Balance, December 31, 2013	118,190		149,381		267,571		63.53		9.3
Granted	24,000		44,750		68,750
Vested	41,729		(41,729	)	—
Converted	(2,000	)	—		(2,000	)
Cancelled	—		(1,335	)	(1,335	)
Balance, December 31, 2014	181,919		151,067		332,986		71.14		10.5
Granted	—		—		—
Vested	36,650		(36,650	)	—
Converted	(74,384	)	—		(74,384	)
Cancelled	—		(8,260	)	(8,260	)
Balance, December 31, 2015	144,185		106,157		250,342		$	75.41	9.5