Income Taxes (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Income before income taxes for U.S. operations	$ 573.1	$ 1,241.1	$ 1,051.4
Income before income taxes for foreign operations	(6.3)	10.9	12.6
Net operating loss carryforwards	21.0
Remaining state loss carryforwards	6.5
Additions for tax positions related to the current year	0.0	5.5	5.0
Additions for tax positions of prior years	1.0	0.0	2.5
Reduction in tax positions of prior years	26.6	0.7	0.1
Unrecognized tax benefits including interest and penalties that would affect the Company's effective tax rate if recognized	13.1	13.9
Total accrued interest and penalties related to uncertain tax positions	8.9	12.4
Increase (decrease) in income tax expense related to interest and penalties on unrecognized tax benefits	3.5	$ 0.8	$ 0.8
Settlement with taxing authority and lapse in statute of limitations
Income Tax Contingency [Line Items]
Reasonably possible decrease in unrecognized federal and state tax benefits within twelve months	$ 24.4