Years Subject to Examination (Details)	12 Months Ended
	Dec. 31, 2019
Federal
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2005, 2008, 2010, 2011, 2012, 2013, 2016, 2017 and 2018
Montana
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2016, 2017 and 2018
Idaho
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2016, 2017 and 2018
Utah
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2016, 2017 and 2018
Colorado
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2010, 2011, 2012, 2015, 2016, 2017 and 2018
Arizona
Income Tax Examination
Income tax return jurisdictions and years that remain subject to examination	2015, 2016, 2017 and 2018