Columbia Banking System Inc., the Tacoma, Wash.-based parent of Columbia Bank, has reported an 86 percent increase in its net income in 2011, compared with 2010, attributing the surge to three acquisitions and organic growth.

The bank company reported net income of $48 million, or $1.21 a diluted share, for last year, up from $25.8 million, or 72 cents a share, the prior year.

Melanie Dressel, Columbia's president and CEO, says the company's total assets increased 13 percent, to $4.79 billion on Dec. 31 from $4.26 billion a year earlier. The growth in assets occurred largely due to its Federal Deposit Insurance Corp.-assisted acquisitions of First Heritage Bank and Summit Bank during the second quarter of 2011 and of certain Bank of Whitman assets later that year.

In addition to increasing the bank's total assets, the acquisitions contributed to a 21 percent increase in the number of Columbia branches. The company had 102 branches in Washington state and Oregon at the end of last year.

"2011 was an exceptional year of growth and opportunity for us," Dressel says.

Total loans not covered under the FDIC loss-sharing agreements were $2.35 billion as of Dec. 31, up 23 percent from $1.92 billion a year earlier. The bank reported that its loan portfolio is 44 percent commercial business loans, 41 percent commercial real estate, 8 percent consumer, 4 percent construction loans—both residential and commercial—and 3 percent multifamily real estate.

Columbia reports that its nonperforming assets shrunk to $85.4 million as of Dec. 31, down from $89.3 million at the end of the previous quarter and from $120.2 million a year earlier.

Its return on average assets for 2011 was 1.07 percent, up from 0.72 percent a year earlier.