LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Loans by Geographic Type) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 3,240,321	$ 3,235,714	$ 3,229,662
Percent of total loans	100.00%	100.00%	100.00%
Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,187,031
Percent of total loans	67.50%
Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	673,038
Percent of total loans	20.80%
Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	277,495
Percent of total loans	8.50%
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	102,757
Percent of total loans	3.20%
Commerical real estate - owner-occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	497,442	489,581	468,318
Percent of total loans	15.30%	15.10%	14.50%
Commerical real estate - owner-occupied [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	376,330
Commerical real estate - owner-occupied [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	58,671
Commerical real estate - owner-occupied [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	57,363
Commerical real estate - owner-occupied [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,078
Commerical real estate - investment properties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	602,761	583,641	612,617
Percent of total loans	18.60%	18.00%	19.00%
Commerical real estate - investment properties [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	467,720
Commerical real estate - investment properties [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	87,184
Commerical real estate - investment properties [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	43,750
Commerical real estate - investment properties [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,107
Multifamily real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	134,290	137,504	132,306
Percent of total loans	4.10%	4.30%	4.10%
Multifamily real estate [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	112,625
Multifamily real estate [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	13,208
Multifamily real estate [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,196
Multifamily real estate [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	261
Commercial construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	34,762	30,229	40,276
Percent of total loans	1.10%	0.90%	1.20%
Commercial construction [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	23,636
Commercial construction [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,566
Commercial construction [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,207
Commercial construction [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,353
Multifamily construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	34,147	22,581	20,654
Percent of total loans	1.10%	0.70%	0.60%
Multifamily construction [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	15,566
Multifamily construction [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	18,581
Multifamily construction [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
Multifamily construction [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
One-to four-family construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	171,876	160,815	148,717
Percent of total loans	5.30%	5.00%	4.60%
One-to four-family construction [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	97,016
One-to four-family construction [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	72,729
One-to four-family construction [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,131
One-to four-family construction [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
Land and land development - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	78,446	77,010	89,329
Percent of total loans	2.40%	2.40%	2.70%
Land and land development - residential [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	47,106
Land and land development - residential [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	29,614
Land and land development - residential [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,726
Land and land development - residential [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
Land and land development - commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	12,477	13,982	12,044
Percent of total loans	0.40%	0.40%	0.40%
Land and land development - commercial [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	7,482
Land and land development - commercial [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,043
Land and land development - commercial [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,952
Land and land development - commercial [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	619,478	618,049	609,497
Percent of total loans	19.10%	19.10%	18.90%
Commercial business [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	393,638
Commercial business [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	83,574
Commercial business [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	55,047
Commercial business [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	87,219
Agricultural business, including secured by farming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	210,225	230,031	188,955
Percent of total loans	6.50%	7.10%	5.90%
Agricultural business, including secured by farming [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	105,886
Agricultural business, including secured by farming [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	38,934
Agricultural business, including secured by farming [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	65,405
Agricultural business, including secured by farming [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
One- to four-family real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	566,730	581,670	619,511
Percent of total loans	17.50%	18.00%	19.20%
One- to four-family real estate [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	352,209
One- to four-family real estate [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	188,804
One- to four-family real estate [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	23,660
One- to four-family real estate [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,057
Total consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	277,687	290,621
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	112,382	120,498	106,978
Percent of total loans	3.50%	3.70%	3.30%
Consumer [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	76,807
Consumer [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	30,233
Consumer [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,337
Consumer [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5
Consumer secured by one- to four-family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	165,305	170,123	180,460
Percent of total loans	5.10%	5.30%	5.60%
Consumer secured by one- to four-family [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	111,010
Consumer secured by one- to four-family [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	41,897
Consumer secured by one- to four-family [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	11,721
Consumer secured by one- to four-family [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 677