Share and Unit-Based Plans: (Tables)

9 Months Ended

Sep. 30, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Compensation cost under the share and unit-based plans

The following summarizes the compensation cost under the share and unit-based plans:

	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
	2015		2014		2015		2014
LTIP Units	$	3,812	$	3,465	$	22,810	$	25,133
Stock awards	28		84		225		281
Stock units	881		1,134		5,214		3,775
Stock options	4		4		12		12
Phantom stock units	248		296		827		902
	$	4,973	$	4,983	$	29,088	$	30,103

Summary of activity of non-vested LTIP Units, stock awards, phantom stock and stock units

The following table summarizes the activity of the non-vested LTIP Units, stock awards, phantom stock units and stock units:

	LTIP Units				Stock Awards				Phantom Stock Units				Stock Units
	Units		Value(1)		Shares		Value(1)		Units		Value(1)		Units		Value(1)
Balance at January 1, 2015	46,695		$	58.89	9,189		$	59.25	9,269		$	58.35	144,374		$	59.94
Granted	368,508		75.98		—		—		7,056		80.68		76,531		86.61
Vested	(132,607	)	86.72		(7,410	)	58.65		(11,839	)	70.82		(84,498	)	61.14
Forfeited	—		—		—		—		(2,458	)	55.62		—		—
Balance at September 30, 2015	282,596		$	68.12	1,779		$	61.72	2,028		$	66.52	136,407		$	74.66

(1) Value represents the weighted average grant date fair value.

Summary of activity of SARs and stock options outstanding

The following table summarizes the activity of the stock appreciations rights ("SARs") and stock options outstanding:

	SARs				Stock Options
	Shares		Value(1)		Shares	Value(1)
Balance at January 1, 2015	772,639		$	56.67	10,068	$	59.57
Granted	—		—		—	—
Exercised	(344,981	)	56.88		—	—
Forfeited	—		—		—	—
Balance at September 30, 2015	427,658		$	56.50	10,068	$	59.57

(1) Value represents the weighted average exercise price.