Income Taxes (Details) (USD $)			3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended			3 Months Ended	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012 Internal Revenue Service (IRS)	Jun. 30, 2013 Internal Revenue Service (IRS)	Dec. 31, 2012 Colorado	Jun. 30, 2013 Colorado	Jun. 30, 2013 Minnesota	Jun. 30, 2013 Texas	Mar. 31, 2013 Wisconsin	Jun. 30, 2013 Wisconsin
Tax Audits [Abstract]
Year(s) no longer subject to audit as statute of limitations has expired				2008
Earliest year subject to examination				2009		2006	2009	2008		2008
Year(s) under examination			2010 and 2011		2006 through 2009		None	None	2009 through 2011
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions	$ 7,600,000	$ 4,700,000
Unrecognized tax benefit — Temporary tax positions	31,700,000	29,800,000
Total unrecognized tax benefit	39,300,000	34,500,000
NOL and tax credit carryforwards	(38,100,000)	(33,500,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible	(35,000,000)
Amounts accrued for penalties related to unrecognized tax benefits	$ 0	$ 0