Years Subject to Examination (Details)	12 Months Ended
	Dec. 31, 2016
Federal
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2013, 2014 and 2015
Montana
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2013, 2014 and 2015
Idaho
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2013, 2014 and 2015
Colorado
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2012, 2013, 2014 and 2015
Utah
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2013, 2014 and 2015