Condensed Financial Information (Parent Company Only) (Tables)

12 Months Ended

Dec. 31, 2020

Condensed Financial Information Disclosure [Abstract]

Schedule of Condensed Financial Statements

Following is condensed financial information of First Interstate BancSystem, Inc.

December 31,	2020		2019
Condensed balance sheets:
Cash and cash equivalents	$	123.2	$	147.1
Investment in bank subsidiary	1,986.6		1,899.3
Advances to subsidiaries, net	41.0		48.9
Other assets	61.3		61.7
Total assets	$	2,212.1	$	2,157.0
Other liabilities	$	66.7	$	56.2
Long-term debt	98.6		—
Subordinated debentures held by subsidiary trusts	87.0		86.9
Total liabilities	252.3		143.1
Stockholders’ equity	1,959.8		2,013.9
Total liabilities and stockholders’ equity	$	2,212.1	$	2,157.0

Years Ended December 31,	2020		2019		2018
Condensed statements of income:
Dividends from subsidiaries	$	130.0	$	178.0	$	148.5
Other interest income	0.1		0.3		0.1
Other income, primarily management fees from subsidiaries	28.7		25.9		17.0
Total income	158.8		204.2		165.6
Salaries and benefits	31.5		34.2		25.3
Interest expense	6.6		4.7		4.5
Acquisition expenses	—		17.0		8.1
Other operating expenses, net	15.6		14.8		14.5
Total expenses	53.7		70.7		52.4
Earnings before income tax benefit	105.1		133.5		113.2
Income tax benefit	(6.1)		(11.9)		(9.3)
Income before undistributed earnings of subsidiaries	111.2		145.4		122.5
Undistributed earnings of subsidiaries	50.0		35.6		37.7
Net income	$	161.2	$	181.0	$	160.2

Years Ended December 31,	2020		2019		2018
Condensed statements of cash flows:
Cash flows from operating activities:
Net income	$	161.2	$	181.0	$	160.2
Adjustments to reconcile net income to cash provided by operating activities:
Undistributed earnings of subsidiaries	(50.0)		(35.6)		(37.7)
Stock-based compensation expense	7.5		8.0		5.6
Other, net	(13.6)		8.1		16.4
Net cash provided by operating activities	105.1		161.5		144.5
Cash flows from investing activities:
Acquisition of bank holding company, net of cash and cash equivalents received	—		—		(14.7)
Net cash used in investing activities	—		—		(14.7)

Years Ended December 31,	2020		2019		2018
Cash flows from financing activities:
Net (decrease) increase in advances from subsidiaries	16.7		(6.6)		(9.9)
Proceeds from issuance of long-term debt	98.6		—		—
Repayment of long-term debt	—		—		(26.0)
Proceeds from issuance of common stock, net of stock issuance costs	1.1		1.0		1.8
Purchase and retirement of common stock	(116.8)		(2.5)		(1.0)
Dividends paid to common stockholders	(128.6)		(79.2)		(64.1)
Net cash used in financing activities	(129.0)		(87.3)		(99.2)
Net change in cash and cash equivalents	(23.9)		74.2		30.6
Cash and cash equivalents, beginning of year	147.1		72.9		42.3
Cash and cash equivalents, end of year	$	123.2	$	147.1	$	72.9