Share and Unit-Based Plans - Nonvested Equity Awards (Details)	9 Months Ended
	Sep. 30, 2015 $ / shares shares
LTIP Units
Units (in shares)
Balance at beginning of period (in shares) | shares	46,695
Granted (in shares) | shares	368,508
Vested (in shares) | shares	(132,607)
Forfeited (in shares) | shares	0
Balance at end of period (in shares) | shares	282,596
Value (in dollars per share)
Balance at beginning of period (in dollars per share)	$ 58.89
Granted (in dollars per share)	75.98
Vested (in dollars per share)	86.72
Forfeited (in dollars per share)	0.00
Balance at end of period (in dollars per share)	$ 68.12
Stock awards
Units (in shares)
Balance at beginning of period (in shares) | shares	9,189
Granted (in shares) | shares	0
Vested (in shares) | shares	(7,410)
Forfeited (in shares) | shares	0
Balance at end of period (in shares) | shares	1,779
Value (in dollars per share)
Balance at beginning of period (in dollars per share)	$ 59.25
Granted (in dollars per share)	0.00
Vested (in dollars per share)	58.65
Forfeited (in dollars per share)	0.00
Balance at end of period (in dollars per share)	$ 61.72
Phantom stock units
Units (in shares)
Balance at beginning of period (in shares) | shares	9,269
Granted (in shares) | shares	7,056
Vested (in shares) | shares	(11,839)
Forfeited (in shares) | shares	(2,458)
Balance at end of period (in shares) | shares	2,028
Value (in dollars per share)
Balance at beginning of period (in dollars per share)	$ 58.35
Granted (in dollars per share)	80.68
Vested (in dollars per share)	70.82
Forfeited (in dollars per share)	55.62
Balance at end of period (in dollars per share)	$ 66.52
Stock units
Units (in shares)
Balance at beginning of period (in shares) | shares	144,374
Granted (in shares) | shares	76,531
Vested (in shares) | shares	(84,498)
Forfeited (in shares) | shares	0
Balance at end of period (in shares) | shares	136,407
Value (in dollars per share)
Balance at beginning of period (in dollars per share)	$ 59.94
Granted (in dollars per share)	86.61
Vested (in dollars per share)	61.14
Forfeited (in dollars per share)	0.00
Balance at end of period (in dollars per share)	$ 74.66