Business combinations (Tables)

6 Months Ended

Jun. 30, 2014

Business Acquisition, Supplemental Pro Forma Information [Line Items]

Business Acquisition, Pro Forma Information [Table Text Block]

The following table presents certain unaudited pro forma information for the six month period ended June 30, 2013, for illustrative purposes only. This unaudited pro forma information was calculated as if West Coast had been acquired as of the beginning of the year prior to the acquisition. The unaudited estimated pro forma information combines the historical results of West Coast with the Company’s consolidated historical results and includes certain adjustments reflecting the estimated impact of certain fair value adjustments for the respective periods. 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 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
	Six Months Ended June 30,
	2013
	(in thousands)
Total revenues (net interest income plus noninterest income)	$	177,970
Net income	$	43,256
Earnings per share - basic	$	0.85
Earnings per share - diluted	$	0.83