Share and Unit-Based Plans - Nonvested equity awards (Details)	6 Months Ended
	Jun. 30, 2019 $ / shares shares
LTIP Units
Units
Balance at beginning of period (in shares) | shares	661,578
Granted (in shares) | shares	332,584
Vested (in shares) | shares	(7,654)
Forfeited (in shares) | shares	(14,635)
Balance at end of period (in shares) | shares	971,873
Value
Balance at beginning of period (in dollars per share) | $ / shares	$ 48.38
Granted (in dollars per share) | $ / shares	32.70
Vested (in dollars per share) | $ / shares	59.85
Forfeited (in dollars per share) | $ / shares	34.26
Balance at end of period (in dollars per share) | $ / shares	$ 43.13
Phantom Stock Units
Units
Balance at beginning of period (in shares) | shares	0
Granted (in shares) | shares	19,772
Vested (in shares) | shares	(8,154)
Forfeited (in shares) | shares	0
Balance at end of period (in shares) | shares	11,618
Value
Balance at beginning of period (in dollars per share) | $ / shares	$ 0
Granted (in dollars per share) | $ / shares	42.65
Vested (in dollars per share) | $ / shares	44.36
Forfeited (in dollars per share) | $ / shares	0
Balance at end of period (in dollars per share) | $ / shares	$ 41.45
Stock Units
Units
Balance at beginning of period (in shares) | shares	129,457
Granted (in shares) | shares	90,266
Vested (in shares) | shares	(81,785)
Forfeited (in shares) | shares	(2,531)
Balance at end of period (in shares) | shares	135,407
Value
Balance at beginning of period (in dollars per share) | $ / shares	$ 64.21
Granted (in dollars per share) | $ / shares	41.96
Vested (in dollars per share) | $ / shares	64.27
Forfeited (in dollars per share) | $ / shares	50.62
Balance at end of period (in dollars per share) | $ / shares	$ 49.60