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Accumulated Other Comprehensive Income | 12 Months Ended
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Dec. 31, 2019
Accumulated Other Comprehensive Income [Abstract] |
Comprehensive Income (Loss) Note [Text Block] | Accumulated Other Comprehensive Income The following table shows changes in accumulated other comprehensive income (loss) by component for the years ended December 31, 2019, 2018 and 2017:
|  | Unrealized Gains and Losses on Available for Sale Securities (1) |  | Unrealized Gains and Losses on Pension Plan Liability (1) |  | Unrealized Gains and Losses on Hedging Instruments (1) |  | Total (1)
Year Ended December 31, 2019 |  | (in thousands)
Beginning balance |  | $ | (33,128 | ) |  | $ | (2,177 | ) |  | $ | — |  |  | $ | (35,305 | )
Other comprehensive income (loss) before reclassifications |  | 67,802 |  |  | (2,042 | ) |  | 11,760 |  |  | 77,520 |
Amounts reclassified from accumulated other comprehensive loss (2) |  | (1,636 | ) |  | 245 |  |  | (457 | ) |  | (1,848 | )
Net current-period other comprehensive income (loss) |  | 66,166 |  |  | (1,797 | ) |  | 11,303 |  |  | 75,672 |
Ending balance |  | $ | 33,038 |  |  | $ | (3,974 | ) |  | $ | 11,303 |  |  | $ | 40,367 |
Year Ended December 31, 2018 |  |  |  |  |  |  |  |
Beginning balance |  | $ | (19,779 | ) |  | $ | (2,446 | ) |  | $ | — |  |  | $ | (22,225 | )
Adjustment pursuant to adoption of ASU 2016-01 |  | 157 |  |  | — |  |  | — |  |  | 157 |
Other comprehensive income (loss) before reclassifications |  | (13,425 | ) |  | 24 |  |  | — |  |  | (13,401 | )
Amounts reclassified from accumulated other comprehensive loss (2) |  | (81 | ) |  | 245 |  |  | — |  |  | 164 |
Net current-period other comprehensive income (loss) |  | (13,506 | ) |  | 269 |  |  | — |  |  | (13,237 | )
Ending balance |  | $ | (33,128 | ) |  | $ | (2,177 | ) |  | $ | — |  |  | $ | (35,305 | )
Year Ended December 31, 2017 |  |  |  |  |  |  |  |
Beginning balance |  | $ | (12,704 | ) |  | $ | (6,295 | ) |  | $ | — |  |  | $ | (18,999 | )
Other comprehensive income (loss) before reclassifications |  | (3,391 | ) |  | 4,017 |  |  | — |  |  | 626 |
Amounts reclassified from accumulated other comprehensive loss (2) |  | 7 |  |  | 223 |  |  | — |  |  | 230 |
Net current-period other comprehensive income (loss) |  | (3,384 | ) |  | 4,240 |  |  | — |  |  | 856 |
Adjustment pursuant to adoption of ASU 2018-02 |  | $ | (3,691 | ) |  | $ | (391 | ) |  | $ | — |  |  | $ | (4,082 | )
Ending balance |  | $ | (19,779 | ) |  | $ | (2,446 | ) |  | $ | — |  |  | $ | (22,225 | )
__________ (1) All amounts are net of tax. Amounts in parenthesis indicate debits. (2) See following table for details about these reclassifications. In December 2017, the Company made an election to reclassify income tax effects related to the Tax Cuts and Jobs Act of $4.1 million from accumulated other comprehensive income to retained earnings. The Company uses the portfolio approach to account for the tax consequences of amounts reported in OCI. The following table shows details regarding the reclassifications from accumulated other comprehensive income for the years ended December 31, 2019, 2018 and 2017:
|  | Amount Reclassified from Accumulated Other Comprehensive Income |  | Affected line Item in the Consolidated Statement of Income
|  | Years Ended December 31, |  |
|  | 2019 |  | 2018 |  | 2017 |  |
|  | (in thousands) |  |
Unrealized gains and losses on available for sale debt securities |  | $ | 2,132 |  |  | $ | 106 |  |  | $ | (11 | ) |  | Investment securities gains (losses), net
|  | 2,132 |  |  | 106 |  |  | (11 | ) |  | Total before tax
|  | (496 | ) |  | (25 | ) |  | 4 |  |  | Income tax provision
|  | $ | 1,636 |  |  | $ | 81 |  |  | $ | (7 | ) |  | Net of tax
Amortization of pension plan liability actuarial losses |  | $ | (319 | ) |  | $ | (319 | ) |  | $ | (350 | ) |  | Compensation and employee benefits
|  | (319 | ) |  | (319 | ) |  | (350 | ) |  | Total before tax
|  | 74 |  |  | 74 |  |  | 127 |  |  | Income tax provision
|  | $ | (245 | ) |  | $ | (245 | ) |  | $ | (223 | ) |  | Net of tax
Unrealized gains from hedging instruments |  | $ | 595 |  |  | $ | — |  |  | $ | — |  |  | Loans
|  | 595 |  |  | — |  |  | — |  |  | Total before tax
|  | (138 | ) |  | — |  |  | — |  |  | Income tax provision
|  | $ | 457 |  |  | $ | — |  |  | $ | — |  |  | Net of tax

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- Definition Accumulated Other Comprehensive Income [Abstract] + References No definition available. + Details
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- Definition Accumulated Other Comprehensive Income (Loss) + References No definition available. + Details
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Namespace Prefix: | colb_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration