Federal and state income taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits	$ 3.9		$ 4.3
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	1.2		1.8
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	1.0
Unrecognized Tax Benefits, Income Tax Penalities and Interest Accrued that Would Impact the Effective Tax Rate	0.7
Effective Income Tax Rate, Continuing Operations	38.90%	4.60%
Income Tax Election Impact, Amount		15.7
Effective Income Tax Rate, Excluding Income Tax Election Impact		43.50%
Unrecognized Tax Benefits, Reductions Resulting from Lapse of Applicable Statute of Limitations	$ 0.2
Unrecognized Tax Benefits Change in Next Twelve Months	12 months