Business combinations (Tables)

3 Months Ended

Mar. 31, 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 three month period ended March 31, 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
	Three Months Ended March 31,
	2014
	(in thousands except per share)
Total revenues (net interest income plus noninterest income)	$	97,488
Net income	$	21,078
Earnings per share - basic	$	0.38
Earnings per share - diluted	$	0.37

Intermountain Community Bancorp [Member]

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 months ended March 31, 2015 to the various components of noninterest expense:

	Three Months Ended March 31,
	2015
	(in thousands)
Noninterest Expense
Compensation and employee benefits	$	273
Occupancy	499
Advertising and promotion	96
Data processing and communications	1,558
Legal and professional fees	385
Other	91
Total impact of acquisition-related costs to noninterest expense	$	2,902