Condensed Consolidated Statements of Comprehensive Income (Parentheticals) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Unrealized (losses) gains net of tax benefits of $0.5 and $0.2 during the three and nine months ended September 30, 2017, respectively, and tax provision of $0.3 and benefit of $0.4 for the corresponding periods of the fiscal year ended December 31, 2016 (fiscal 2016), respectively	$ 0.5	$ (0.3)	$ 0.2	$ 0.4
Reclassification adjustment for realized net gains included in net income, net of tax provision of $0.9 during both the three and nine months ended September 2017, respectively, and net of tax provisions of zero and $0.5 for the corresponding periods of fiscal 2016, respectively	0.9	0.0	0.9	0.5
Unrealized gains (loss) net of tax provisions of $0.5 and $3.0, for the three and nine months ended September 30, 2017, respectively, and tax provisions of $0.6 and $1.2 for the corresponding periods of fiscal 2016, respectively	(0.5)	(0.6)	(3.0)	(1.2)
Reclassification adjustment for realized net gains included in net income, net of tax provisions of $0.8 and $1.7 during the three and nine months ended September 30, 2017, respectively, and tax provisions of $0.3 and $0.4 for the corresponding periods of fiscal 2016, respectively	$ 0.8	$ 0.3	$ 1.7	$ 0.4