Incentive Plan Incentive Plan (Long-Term Incentive Units) (Details) - Long-Term Incentive Units - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares:
Unvested, beginning of period (in shares)	278,301
Granted (in shares)	29,544
Vested (in shares)	(175,975)
Cancelled or expired (in shares)	(3,048)
Unvested, end of period (in shares)	128,822	278,301
Weighted-Average Grant Date Fair Value
Unvested, beginning of period (in dollars per share)	$ 62.85
Granted (in dollars per share)	87.18
Vested (in dollars per share)	64.35
Cancelled (in dollars per share)	54.48
Unvested, end of period (in dollars per share)	$ 66.58	$ 62.85
Share/unit compensation expense	$ 4.5	$ 5.9	$ 12.6
Capitalized expense related to construction and leasing activities	1.8	1.2	$ 1.7
Unearned compensation	$ 5.6	$ 9.9
Unearned compensation, period of recognition	2 years 27 days