Loans - Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Allowance	$ 9,807,500,000	$ 8,930,700,000
Loans and Leases Receivable, Net of Deferred Income		8,936,200,000
Loans and Leases Receivable, Commitments to Purchase or Sell	0
Proceeds from Sale of Loans and Leases Held-for-investment	0
FIBK Commercial Real Estate Non Owner Occupied Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	511,900,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	309,900,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	218,100,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	109,500,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	147,200,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(364,100,000)
Financing Receivable, Revolving	13,800,000
Loans and Leases Receivable, Allowance	1,674,500,000
Commercial Real Estate Owner Occupied
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	432,500,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	328,600,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	227,500,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	130,700,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	187,400,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(389,100,000)
Financing Receivable, Revolving	9,200,000
Loans and Leases Receivable, Allowance	1,705,000,000.0
Commercial Real Estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		3,487,800,000
Commercial Real Estate Multifamily
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	132,500,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	58,900,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	23,500,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	41,600,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	25,800,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(80,600,000)
Financing Receivable, Revolving	800,000
Loans and Leases Receivable, Allowance	363,700,000
Land Acquisition And Development Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	265,000,000.0	302,100,000
Financing Receivable, Originated in Current Fiscal Year	105,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	58,900,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	27,600,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	31,700,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	7,600,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(27,700,000)
Financing Receivable, Revolving	6,400,000
Loans and Leases Receivable, Allowance	265,000,000.0
Loans and Leases Receivable, Net of Deferred Income		302,100,000
Residential Real Estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		1,246,100,000
Commercial Real Estate Construction [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	523,500,000	431,500,000
Financing Receivable, Originated in Current Fiscal Year	236,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	195,400,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	62,700,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	11,900,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	6,000,000.0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(200,000)
Financing Receivable, Revolving	11,600,000
Loans and Leases Receivable, Allowance	523,500,000
Loans and Leases Receivable, Net of Deferred Income		431,500,000
Residential Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	250,900,000	244,100,000
Financing Receivable, Originated in Current Fiscal Year	80,600,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	64,700,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	16,700,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	5,600,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(100,000)
Financing Receivable, Revolving	83,200,000
Loans and Leases Receivable, Allowance	250,900,000
Loans and Leases Receivable, Net of Deferred Income		244,100,000
Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	220,600,000	226,600,000
Financing Receivable, Originated in Current Fiscal Year	54,200,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	58,200,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	32,600,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	19,600,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	17,000,000.0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(32,600,000)
Financing Receivable, Revolving	6,400,000
Loans and Leases Receivable, Allowance	220,600,000
Loans and Leases Receivable, Net of Deferred Income		226,600,000
Commercial and Floor Plans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	1,044,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	156,200,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	142,200,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	77,200,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	51,100,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(96,500,000)
Financing Receivable, Revolving	247,200,000
Loans and Leases Receivable, Allowance	1,814,500,000
Commercial Purpose Secured by 1-4 Family
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	85,200,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	55,200,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	38,800,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	21,100,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	17,400,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(36,700,000)
Financing Receivable, Revolving	18,400,000
Loans and Leases Receivable, Allowance	272,800,000
Agriculture
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	52,600,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	20,300,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	15,300,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	4,800,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	3,200,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(2,000,000.0)
Financing Receivable, Revolving	147,900,000
Loans and Leases Receivable, Allowance	246,100,000
Residential Real Estate 1-4 Family
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	491,200,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	114,600,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	57,200,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	47,800,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	65,700,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(235,800,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	1,012,300,000
Residential Real Estate 1-4 Family | Performing Financial Instruments
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	491,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	113,900,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	57,200,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	47,800,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	65,700,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(234,600,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	1,010,300,000
Residential Real Estate 1-4 Family | Nonperforming Financial Instruments
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	700,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(1,200,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	2,000,000.0
Home Equity Loan
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	12,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	7,300,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	7,100,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	9,700,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	4,800,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(14,800,000)
Financing Receivable, Revolving	328,200,000
Loans and Leases Receivable, Allowance	384,000,000.0
Home Equity Loan | Performing Financial Instruments
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	12,000,000.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	7,100,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	7,100,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	9,700,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	4,700,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(14,400,000)
Financing Receivable, Revolving	328,100,000
Loans and Leases Receivable, Allowance	383,100,000
Home Equity Loan | Nonperforming Financial Instruments
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	200,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	100,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(400,000)
Financing Receivable, Revolving	100,000
Loans and Leases Receivable, Allowance	900,000
Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	805,100,000	784,600,000
Financing Receivable, Originated in Current Fiscal Year	334,600,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	188,100,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	118,000,000.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	74,000,000.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	47,700,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(42,700,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	805,100,000
Loans and Leases Receivable, Net of Deferred Income		784,600,000
Indirect consumer | Performing Financial Instruments
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	334,500,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	187,900,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	117,900,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	73,800,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	47,600,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(42,600,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	804,300,000
Indirect consumer | Nonperforming Financial Instruments
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	200,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	100,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	200,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	100,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(100,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	800,000
Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	150,600,000	179,000,000.0
Financing Receivable, Originated in Current Fiscal Year	47,200,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	29,400,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	28,200,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	11,900,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	5,300,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(8,600,000)
Financing Receivable, Revolving	20,000,000.0
Loans and Leases Receivable, Allowance	150,600,000
Loans and Leases Receivable, Net of Deferred Income		1,045,200,000
Other consumer | Performing Financial Instruments
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	47,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	29,400,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	28,100,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	11,900,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	5,300,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(8,600,000)
Financing Receivable, Revolving	19,900,000
Loans and Leases Receivable, Allowance	150,300,000
Other consumer | Nonperforming Financial Instruments
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	100,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0
Financing Receivable, Revolving	100,000
Loans and Leases Receivable, Allowance	300,000
Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,025,900,000	1,045,200,000
Loans and Leases Receivable, Net of Deferred Income		179,000,000.0
Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	70,200,000	81,600,000
Financing Receivable, Originated in Current Fiscal Year	138.3
Loans and Leases Receivable, Net of Deferred Income		81,600,000
Credit card consumer | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	70.2
Credit card consumer | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	66.6
Credit card consumer | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	1.5
Credit card consumer | Performing Financial Instruments
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	137.4
Credit card consumer | Performing Financial Instruments | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	69.6
Credit card consumer | Performing Financial Instruments | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	66.3
Credit card consumer | Performing Financial Instruments | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	1.5
Credit card consumer | Nonperforming Financial Instruments
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	0.9
Credit card consumer | Nonperforming Financial Instruments | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	0.6
Credit card consumer | Nonperforming Financial Instruments | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	0.3
Credit card consumer | Nonperforming Financial Instruments | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	0
Construction Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		977,700,000
Real Estate Loan
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		5,938,200,000
Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,153,900,000	1,673,700,000
Loans and Leases Receivable, Net of Deferred Income		1,673,700,000
Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	247,600,000	279,100,000
Loans and Leases Receivable, Net of Deferred Income		279,100,000
Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3,743,200,000	3,487,800,000
Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,039,400,000	977,700,000
Residential Mortgage [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,396,300,000	1,246,100,000
Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	6,399,500,000	5,938,200,000
Other Assets Especial Mentioned
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		157,500,000
Other Assets Especial Mentioned | FIBK Commercial Real Estate Non Owner Occupied Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	300,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,300,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	900,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	100,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	6,400,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(13,700,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	23,700,000
Other Assets Especial Mentioned | Commercial Real Estate Owner Occupied
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	7,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	9,600,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,800,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	3,100,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	18,600,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(20,000,000.0)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	63,200,000
Other Assets Especial Mentioned | Commercial Real Estate Multifamily
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(100,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	100,000
Other Assets Especial Mentioned | Land Acquisition And Development Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		3,800,000
Financing Receivable, Originated in Current Fiscal Year	200,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	100,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	900,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(1,200,000)
Financing Receivable, Revolving	500,000
Loans and Leases Receivable, Allowance	2,900,000
Other Assets Especial Mentioned | Commercial Real Estate Construction [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		1,700,000
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,500,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	1,500,000
Other Assets Especial Mentioned | Residential Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		900,000
Other Assets Especial Mentioned | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		14,300,000
Financing Receivable, Originated in Current Fiscal Year	2,800,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	6,700,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,000,000.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	1,500,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	900,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(1,000,000.0)
Financing Receivable, Revolving	500,000
Loans and Leases Receivable, Allowance	14,400,000
Other Assets Especial Mentioned | Commercial and Floor Plans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	5,600,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,000,000.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,900,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	7,000,000.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	3,900,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(500,000)
Financing Receivable, Revolving	2,400,000
Loans and Leases Receivable, Allowance	22,300,000
Other Assets Especial Mentioned | Commercial Purpose Secured by 1-4 Family
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	500,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	500,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	300,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	100,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	500,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(800,000)
Financing Receivable, Revolving	800,000
Loans and Leases Receivable, Allowance	3,500,000
Other Assets Especial Mentioned | Agriculture
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	1,500,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	700,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	400,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	100,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(300,000)
Financing Receivable, Revolving	13,400,000
Loans and Leases Receivable, Allowance	16,400,000
Other Assets Especial Mentioned | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		200,000
Other Assets Especial Mentioned | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		400,000
Other Assets Especial Mentioned | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		600,000
Other Assets Especial Mentioned | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		40,400,000
Other Assets Especial Mentioned | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		8,500,000
Other Assets Especial Mentioned | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		84,700,000
Other Assets Especial Mentioned | Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		6,400,000
Other Assets Especial Mentioned | Residential Mortgage [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		2,600,000
Other Assets Especial Mentioned | Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		108,000,000.0
Substandard
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		224,000,000.0
Substandard | FIBK Commercial Real Estate Non Owner Occupied Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	15,700,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,700,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,000,000.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	4,100,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,100,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(13,900,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	38,500,000
Substandard | Commercial Real Estate Owner Occupied
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	8,900,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	6,500,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	11,500,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	5,000,000.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	15,100,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(11,100,000)
Financing Receivable, Revolving	300,000
Loans and Leases Receivable, Allowance	58,400,000
Substandard | Land Acquisition And Development Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		1,900,000
Financing Receivable, Originated in Current Fiscal Year	300,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,200,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	100,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(100,000)
Financing Receivable, Revolving	100,000
Loans and Leases Receivable, Allowance	1,800,000
Substandard | Commercial Real Estate Construction [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		1,500,000
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(100,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	100,000
Substandard | Residential Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		2,200,000
Financing Receivable, Originated in Current Fiscal Year	200,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0
Financing Receivable, Revolving	1,100,000
Loans and Leases Receivable, Allowance	1,300,000
Substandard | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	1,400,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5,900,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	3,400,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	900,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	3,400,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(4,400,000)
Financing Receivable, Revolving	600,000
Loans and Leases Receivable, Allowance	20,000,000.0
Substandard | Commercial and Floor Plans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	8,800,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,800,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,300,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	400,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	4,100,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(1,100,000)
Financing Receivable, Revolving	11,500,000
Loans and Leases Receivable, Allowance	32,000,000.0
Substandard | Commercial Purpose Secured by 1-4 Family
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	2,400,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,000,000.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,800,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	300,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,400,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(1,000,000.0)
Financing Receivable, Revolving	100,000
Loans and Leases Receivable, Allowance	11,000,000.0
Substandard | Agriculture
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	3,700,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,500,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,200,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	600,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	100,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(400,000)
Financing Receivable, Revolving	3,600,000
Loans and Leases Receivable, Allowance	14,100,000
Substandard | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		2,900,000
Substandard | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		800,000
Substandard | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		3,700,000
Substandard | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		60,300,000
Substandard | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		22,700,000
Substandard | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		97,300,000
Substandard | Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		5,600,000
Substandard | Residential Mortgage [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		7,800,000
Substandard | Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		137,300,000
Doubtful
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		5,900,000
Doubtful | FIBK Commercial Real Estate Non Owner Occupied Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	200,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	200,000
Doubtful | Commercial Real Estate Owner Occupied
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	200,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	200,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(100,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	500,000
Doubtful | Land Acquisition And Development Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		1,000,000.0
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(100,000)
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	100,000
Doubtful | Commercial Real Estate Construction [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		0
Doubtful | Residential Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		0
Doubtful | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		0
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	300,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0
Financing Receivable, Revolving	0
Loans and Leases Receivable, Allowance	300,000
Doubtful | Commercial and Floor Plans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	300,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	400,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	100,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(2,600,000)
Financing Receivable, Revolving	200,000
Loans and Leases Receivable, Allowance	3,600,000
Doubtful | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		0
Doubtful | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		100,000
Doubtful | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		100,000
Doubtful | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		3,600,000
Doubtful | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		100,000
Doubtful | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		800,000
Doubtful | Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		1,000,000.0
Doubtful | Residential Mortgage [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		300,000
Doubtful | Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		2,100,000
Total Criticized Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		387,400,000
Total Criticized Loans | Land Acquisition And Development Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		6,700,000
Total Criticized Loans | Commercial Real Estate Construction [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		3,200,000
Total Criticized Loans | Residential Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		3,100,000
Total Criticized Loans | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		40,900,000
Total Criticized Loans | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		3,100,000
Total Criticized Loans | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		1,300,000
Total Criticized Loans | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		4,400,000
Total Criticized Loans | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		104,300,000
Total Criticized Loans | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		31,300,000
Total Criticized Loans | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		182,800,000
Total Criticized Loans | Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		13,000,000.0
Total Criticized Loans | Residential Mortgage [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		10,700,000
Total Criticized Loans | Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		247,400,000
Pass
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		8,548,800,000
Pass | FIBK Commercial Real Estate Non Owner Occupied Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	495,900,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	304,900,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	216,000,000.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	105,300,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	139,700,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(336,500,000)
Financing Receivable, Revolving	13,800,000
Loans and Leases Receivable, Allowance	1,612,100,000
Pass | Commercial Real Estate Owner Occupied
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	416,300,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	312,500,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	211,200,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	122,400,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	153,700,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(357,900,000)
Financing Receivable, Revolving	8,900,000
Loans and Leases Receivable, Allowance	1,582,900,000
Pass | Commercial Real Estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		3,305,000,000.0
Pass | Commercial Real Estate Multifamily
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	132,500,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	58,900,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	23,500,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	41,600,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	25,800,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(80,500,000)
Financing Receivable, Revolving	800,000
Loans and Leases Receivable, Allowance	363,600,000
Pass | Land Acquisition And Development Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	104,600,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	58,800,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	26,400,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	30,700,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	7,600,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(26,300,000)
Financing Receivable, Revolving	5,800,000
Loans and Leases Receivable, Allowance	260,200,000
Loans and Leases Receivable, Net of Deferred Income		295,400,000
Pass | Residential Real Estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		1,235,400,000
Pass | Commercial Real Estate Construction [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	236,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	195,400,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	61,200,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	11,900,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	6,000,000.0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(300,000)
Financing Receivable, Revolving	11,600,000
Loans and Leases Receivable, Allowance	521,900,000
Loans and Leases Receivable, Net of Deferred Income		428,300,000
Pass | Residential Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	80,400,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	64,700,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	16,700,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	5,600,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(100,000)
Financing Receivable, Revolving	82,100,000
Loans and Leases Receivable, Allowance	249,600,000
Loans and Leases Receivable, Net of Deferred Income		241,000,000.0
Pass | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	50,000,000.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	45,300,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	28,200,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	17,200,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	12,700,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(27,200,000)
Financing Receivable, Revolving	5,300,000
Loans and Leases Receivable, Allowance	185,900,000
Loans and Leases Receivable, Net of Deferred Income		185,700,000
Pass | Commercial and Floor Plans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	1,029,400,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	153,000,000.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	136,000,000.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	69,800,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	43,000,000.0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(92,300,000)
Financing Receivable, Revolving	233,100,000
Loans and Leases Receivable, Allowance	1,756,600,000
Pass | Commercial Purpose Secured by 1-4 Family
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	82,300,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	53,700,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	33,700,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	20,700,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	15,500,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(34,900,000)
Financing Receivable, Revolving	17,500,000
Loans and Leases Receivable, Allowance	258,300,000
Pass | Agriculture
Loans and Leases Receivable Recorded Investment, Criticized Loans
Financing Receivable, Originated in Current Fiscal Year	47,400,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	18,100,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	10,700,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	4,200,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	3,000,000.0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	(1,300,000)
Financing Receivable, Revolving	130,900,000
Loans and Leases Receivable, Allowance	$ 215,600,000
Pass | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		781,500,000
Pass | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		1,040,800,000
Pass | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		177,700,000
Pass | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		81,600,000
Pass | Construction Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		964,700,000
Pass | Real Estate Loan
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		5,690,800,000
Pass | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		1,569,400,000
Pass | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans and Leases Receivable, Net of Deferred Income		$ 247,800,000