Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Income Taxes
Deferred tax valuation allowance	$ (8.4)
Balance of deferred tax valuation allowance	$ 250.5		$ 258.9
Overall effective income tax expense (benefit) rate (as a percent)	0.90%	0.00%
Federal
Income Taxes
Period of net operating losses carryforward	20 years
Period of federal tax credit carryforwards	5 years
State | Minimum
Income Taxes
Period of net operating losses carryforward	10 years
State | Maximum
Income Taxes
Period of net operating losses carryforward	20 years