Years Subject to Examination (Details)	12 Months Ended
	Dec. 31, 2014
Federal
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2008, 2009, 2010, 2011, 2012 and 2013
Montana
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2011, 2012 and 2013
Idaho
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2009, 2010, 2011, 2012 and 2013
Colorado
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2008, 2009, 2010, 2011, 2012 and 2013
Utah
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2011, 2012 and 2013