Incentive Plan (Summary of Long-Term Incentive Units) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Weighted-Average Grant Date Fair Value
Award vesting period			4 years
Long-Term Incentive Units
Units
Unvested beginning of period (shares)			276,669
Granted (shares)			28,227
Vested (shares)			(158,844)
Cancelled or expired (shares)			(4,517)
Unvested end of period (shares)	141,535		141,535
Weighted-Average Grant Date Fair Value
Unvested, beginning of period ($ per share)			$ 62.92
Granted ($ per share)			86.82
Vested ($ per share)			63.73
Cancelled or expired ($ per share)			58.11
Unvested, end of period ($ per share)	$ 66.80		$ 66.80
Award vesting period			4 years
Share/unit compensation expense	$ 1.1	$ 1.5	$ 3.8	$ 4.6
Capitalized expense related to construction and leasing activities	0.5	$ 0.0	1.5	$ 1.1
Unearned compensation	$ 6.7		$ 6.7		$ 9.9
Unearned compensation, period of recognition			2 years 1 month 20 days