Summary of Significant Accounting Policies (Intangible Assets - Useful Life) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets
Amortization expense recognized	$ 6.1	$ 5.5	$ 5.0
Amortization expense expected to be incurred, 2016	6.1
Amortization expense expected to be incurred, 2017	6.1
Amortization expense expected to be incurred, 2018	5.9
Amortization expense expected to be incurred, 2019	5.8
Amortization expense expected to be incurred, 2020	5.8
Amortization expense expected to be incurred, after year five	$ 27.7
Minimum
Finite-Lived Intangible Assets
Estimated useful lives (in years)	5 years
Maximum
Finite-Lived Intangible Assets
Estimated useful lives (in years)	20 years