Share and Unit-based Plans - SARs Roll Forward Activity (Details) - SARs - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Units
Balance at beginning of year (shares)	284,146	417,783	772,639
Granted (shares)	0	0	0
Exercised (shares)	(48,707)	(143,822)	(364,807)
Special dividend adjustment (shares)	0	10,185	9,951
Balance at end of year (shares)	235,439	284,146	417,783
Weighted Average Exercise Price (in dollars per share)
Balance at beginning of year (in dollars per share)	$ 53.85	$ 55.13	$ 56.67
Granted (in dollars per share)	0.00	0.00	0.00
Vested (in dollars per share)	53.95	53.73	56.86
Special dividend adjustment (in dollars per share)	0.00	53.88	55.13
Balance at end of year (in dollars per share)	$ 53.83	$ 53.85	$ 55.13