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Business combinations (Tables) | 9 Months Ended
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Sep. 30, 2015
Business Acquisition, Supplemental Pro Forma Information [Line Items] |
Business Acquisition, Pro Forma Information [Table Text Block] | For illustrative purposes only, the following table presents certain unaudited pro forma information for the nine month period ended September 30, 2014. This unaudited pro forma information was calculated as if Intermountain had been acquired as of the beginning of the year prior to the date of acquisition. The unaudited pro forma information combines the historical results of Intermountain with the Company’s consolidated historical results and includes certain adjustments reflecting the estimated impact of certain fair value adjustments for the respective period. The pro forma information is not indicative of what would have occurred had the acquisition occurred as of the beginning of the year prior to the acquisition. In particular, no adjustments have been made to eliminate the impact of other-than-temporary impairment losses and losses recognized on the sale of securities that may not have been necessary had the investment securities been recorded at fair value as of the beginning of the year prior to the date of acquisition. The unaudited pro forma information does not consider any changes to the provision for credit losses resulting from recording loan assets at fair value. Additionally, Columbia expects to achieve further operating cost savings and other business synergies, including revenue growth, as a result of the acquisition which are not reflected in the pro forma amounts that follow. As a result, actual amounts would have differed from the unaudited pro forma information presented.
|  | Unaudited Pro Forma
|  | Nine Months Ended September 30,
|  | 2014
|  | (in thousands except per share)
Total revenues (net interest income plus noninterest income) |  | $ | 300,151 |
Net income |  | $ | 66,788 |
Earnings per share - basic |  | $ | 1.19 |
Earnings per share - diluted |  | $ | 1.18 |
Intermountain Community Bancorp [Member] |
Business Acquisition [Line Items] |
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] | The table below summarizes the amounts recognized as of the acquisition date for each major class of assets acquired and liabilities assumed:
|  | November 1, 2014
|  | (in thousands)
Purchase price as of November 1, 2014 |  | $ | 131,935 |
Recognized amounts of identifiable assets acquired and (liabilities assumed), at fair value: |  |
Cash and cash equivalents |  | $ | 47,283 |
Investment securities |  | 299,458 |
Federal Home Loan Bank stock |  | 2,124 |
Acquired loans |  | 502,595 |
Interest receivable |  | 4,656 |
Premises and equipment |  | 20,696 |
Other real estate owned |  | 2,752 |
Core deposit intangible |  | 10,900 |
Other assets |  | 35,128 |
Deposits |  | (736,795 | )
Other borrowings |  | (22,904 | )
Securities sold under agreements to repurchase |  | (59,043 | )
Other liabilities |  | (13,725 | )
Total fair value of identifiable net assets |  | 93,125 |
Goodwill |  | $ | 38,810 |
Business Acquisition, Supplemental Pro Forma Information [Line Items] |
Business Acquisition, Integration, Restructuring and Other Related Costs [Text Block] | The following table shows the impact of the acquisition-related expenses related to the acquisition of Intermountain for the three and nine month periods ended September 30, 2015 to the various components of noninterest expense:
|  | Three Months Ended September 30, |  | Nine Months Ended September 30,
|  | 2015 |  | 2014 |  | 2015 |  | 2014
|  | (in thousands)
Noninterest Expense |  |  |  |  |  |  |  |
Compensation and employee benefits |  | $ | — |  |  | $ | — |  |  | $ | 3,308 |  |  | $ | — |
Occupancy |  | 181 |  |  | — |  |  | 1,484 |  |  | — |
Advertising and promotion |  | 40 |  |  | 27 |  |  | 383 |  |  | 27 |
Data processing and communications |  | 42 |  |  | — |  |  | 1,780 |  |  | — |
Legal and professional fees |  | 71 |  |  | 388 |  |  | 1,089 |  |  | 388 |
Other |  | 94 |  |  | 44 |  |  | 929 |  |  | 44 |
Total impact of acquisition-related costs to noninterest expense |  | $ | 428 |  |  | $ | 459 |  |  | $ | 8,973 |  |  | $ | 459 |

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- Definition Tabular disclosure of pro forma results of operations for a material business acquisition or series of individually immaterial business acquisitions that are material in the aggregate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(2)-(3) -URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463 + Details
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- Definition Tabular disclosure of the amounts recognized as of the acquisition date for each major class of assets acquired and liabilities assumed. May include but not limited to the following: (a) acquired receivables; (b) contingencies recognized at the acquisition date; and (c) the fair value of noncontrolling interests in the acquiree. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4845-128472 + Details
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