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Condensed Financial Information (Parent Company Only) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Cash flows from operating activities: |  |  |
Net income | $ 161.2 | $ 181.0 | $ 160.2
Adjustments to reconcile net income to cash provided by operating activities: |  |  |
Stock-based compensation expense | 7.5 | 8.0 | 5.6
Net cash provided by operating activities | 268.3 | 127.3 | 219.0
Cash flows from investing activities: |  |  |
Acquisition of banks and bank holding companies, net of cash and cash equivalents received | 0.0 | (298.4) | (28.1)
Net cash used in investing activities | (1,869.8) | (16.8) | (181.1)
Cash flows from financing activities: |  |  |
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 | 2,801.5 | 144.3 | 25.2
Net increase (decrease) in cash and cash equivalents | 1,200.0 | 254.8 | 63.1
Cash and cash equivalents at beginning of period | 1,076.8 | 822.0 | 758.9
Cash and cash equivalents at end of period | 2,276.8 | 1,076.8 | 822.0
Parent Company |  |  |
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 banks and bank holding companies, net of cash and cash equivalents received | 0.0 | 0.0 | (14.7)
Net cash used in investing activities | 0.0 | 0.0 | (14.7)
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 | 0.0 | 0.0
Repayment of long-term debt | 0.0 | 0.0 | (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 increase (decrease) in cash and cash equivalents | (23.9) | 74.2 | 30.6
Cash and cash equivalents at beginning of period | 147.1 | 72.9 | 42.3
Cash and cash equivalents at end of period | 123.2 | 147.1 | 72.9
Community 1st Bank [Member] |  |  |
Cash flows from financing activities: |  |  |
Stock Issued | $ 0.0 |  |
Inland Northwest Bank [Member] |  |  |
Cash flows from financing activities: |  |  |
Stock Issued |  | $ 176.1 |
BOTC Acquisition |  |  |
Cash flows from financing activities: |  |  |
Stock Issued |  |  | $ 173.3

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