Comprehensive Income (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	$ 17.6	$ 14.5	$ 49.0	$ 46.9
Net gain arising during the period, net of tax of $0.9	0	0	1.4	0
Amortization of prior service benefits included in net income, net of tax of $(1.1), $(1.0), $(3.5), $(3.4)	(2.1)	(2.0)	(6.1)	(6.0)
Amortization of net loss included in net income, net of tax of $1.9, $1.4, $5.7, $4.0	3.4	2.3	9.9	6.9
Reclassifiation adjustment for curtailment loss included in net income, net of tax of $1.5	0	0	2.7	0
Other comprehensive income	1.3	0.3	7.9	0.9
Total comprehensive income	18.9	14.8	56.9	47.8
Pension and Other Postretirement Benefit Plans, Tax		0	0.9	0
Amortization, pension and other postretirement benefit plans, net prior service cost recognized in net periodic pension cost, tax effect	(1.1)	(1.0)	(3.5)	(3.4)
Reclassification, pension and other postretirement benefit plans, net gain (loss) recognized in net periodic benefit cost, tax	1.9	1.4	5.7	4.0
Reclassification adjustment for curtailment included in net income, tax	$ 0	$ 0	$ 1.5	$ 0