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Accumulated Other Comprehensive Income | 12 Months Ended
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Dec. 31, 2016
Accumulated Other Comprehensive Income [Abstract] |
Comprehensive Income (Loss) Note [Text Block] | Accumulated Other Comprehensive Loss The following table shows changes in accumulated other comprehensive income (loss) by component for the years ended December 31, 2016, 2015 and 2014:
|  | Unrealized Gains and Losses on Available-for-Sale Securities (1) |  | Unrealized Gains and Losses on Pension Plan Liability (1) |  | Total (1)
Year Ended December 31, 2016 |  | (in thousands)
Beginning balance |  | $ | 386 |  |  | $ | (6,681 | ) |  | $ | (6,295 | )
Other comprehensive loss before reclassifications |  | (12,338 | ) |  | (39 | ) |  | (12,377 | )
Amounts reclassified from accumulated other comprehensive income (2) |  | (752 | ) |  | 425 |  |  | (327 | )
Net current-period other comprehensive income (loss) |  | (13,090 | ) |  | 386 |  |  | (12,704 | )
Ending balance |  | $ | (12,704 | ) |  | $ | (6,295 | ) |  | $ | (18,999 | )
Year Ended December 31, 2015 |  |  |  |  |  |
Beginning balance |  | $ | 7,462 |  |  | $ | (1,841 | ) |  | $ | 5,621 |
Other comprehensive loss before reclassifications |  | (6,069 | ) |  | (5,054 | ) |  | (11,123 | )
Amounts reclassified from accumulated other comprehensive income (2) |  | (1,007 | ) |  | 214 |  |  | (793 | )
Net current-period other comprehensive loss |  | (7,076 | ) |  | (4,840 | ) |  | (11,916 | )
Ending balance |  | $ | 386 |  |  | $ | (6,681 | ) |  | $ | (6,295 | )
Year Ended December 31, 2014 |  |  |  |  |  |
Beginning balance |  | $ | (10,108 | ) |  | $ | (1,936 | ) |  | $ | (12,044 | )
Other comprehensive income before reclassifications |  | 17,922 |  |  | — |  |  | 17,922 |
Amounts reclassified from accumulated other comprehensive income (2) |  | (352 | ) |  | 95 |  |  | (257 | )
Net current-period other comprehensive income |  | 17,570 |  |  | 95 |  |  | 17,665 |
Ending balance |  | $ | 7,462 |  |  | $ | (1,841 | ) |  | $ | 5,621 |
__________ (1) All amounts are net of tax. Amounts in parenthesis indicate debits. (2) See following table for details about these reclassifications. The following table shows details regarding the reclassifications from accumulated other comprehensive income for the years ended December 31, 2016, 2015 and 2014:
|  | Amount Reclassified from Accumulated Other Comprehensive Income |  | Affected line Item in the Consolidated Statement of Income
|  | Years Ended |  |
|  | December 31, 2016 |  | December 31, 2015 |  | December 31, 2014 |  |
|  | (in thousands) |  |
Unrealized gains and losses on available-for-sale securities |  | $ | 1,181 |  |  | $ | 1,581 |  |  | $ | 552 |  |  | Investment securities gains, net
|  | 1,181 |  |  | 1,581 |  |  | 552 |  |  | Total before tax
|  | (429 | ) |  | (574 | ) |  | (200 | ) |  | Income tax provision
|  | $ | 752 |  |  | $ | 1,007 |  |  | $ | 352 |  |  | Net of tax
Amortization of pension plan liability actuarial losses |  | $ | (668 | ) |  | $ | (336 | ) |  | $ | (149 | ) |  | Compensation and employee benefits
|  | (668 | ) |  | (336 | ) |  | (149 | ) |  | Total before tax
|  | 243 |  |  | 122 |  |  | 54 |  |  | Income tax benefit
|  | $ | (425 | ) |  | $ | (214 | ) |  | $ | (95 | ) |  | 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
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Period Type: | duration