LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Loans by Geographic Type) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 3,275,436	$ 3,235,714	$ 3,213,523
Percent of total loans	100.00%	100.00%	100.00%
Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,180,219
Percent of total loans	66.60%
Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	683,796
Percent of total loans	20.90%
Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	288,188
Percent of total loans	8.80%
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	123,233
Percent of total loans	3.70%
Commerical real estate - owner-occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	508,341	489,581	477,871
Percent of total loans	15.50%	15.10%	14.90%
Commerical real estate - owner-occupied [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	384,706
Commerical real estate - owner-occupied [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	58,468
Commerical real estate - owner-occupied [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	59,077
Commerical real estate - owner-occupied [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,090
Commerical real estate - investment properties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	613,757	583,641	604,265
Percent of total loans	18.80%	18.00%	18.80%
Commerical real estate - investment properties [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	467,161
Commerical real estate - investment properties [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	90,518
Commerical real estate - investment properties [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	50,464
Commerical real estate - investment properties [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,614
Multifamily real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	133,770	137,504	138,716
Percent of total loans	4.10%	4.30%	4.30%
Multifamily real estate [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	107,744
Multifamily real estate [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	15,998
Multifamily real estate [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,828
Multifamily real estate [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	200
Commercial construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	18,730	30,229	28,598
Percent of total loans	0.60%	0.90%	0.90%
Commercial construction [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,918
Commercial construction [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,942
Commercial construction [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	377
Commercial construction [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,493
Multifamily construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	33,888	22,581	14,502
Percent of total loans	1.00%	0.70%	0.50%
Multifamily construction [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	22,141
Multifamily construction [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	11,747
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	194,187	160,815	163,521
Percent of total loans	5.90%	5.00%	5.10%
One-to four-family construction [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	108,011
One-to four-family construction [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	84,749
One-to four-family construction [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,427
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	75,576	77,010	79,932
Percent of total loans	2.30%	2.40%	2.50%
Land and land development - residential [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	45,281
Land and land development - residential [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	28,973
Land and land development - residential [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,322
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	11,231	13,982	14,242
Percent of total loans	0.30%	0.40%	0.40%
Land and land development - commercial [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,915
Land and land development - commercial [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,379
Land and land development - commercial [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,937
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	635,658	618,049	603,606
Percent of total loans	19.40%	19.10%	18.80%
Commercial business [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	392,741
Commercial business [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	76,314
Commercial business [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	62,428
Commercial business [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	104,175
Agricultural business, including secured by farming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	223,187	230,031	219,084
Percent of total loans	6.80%	7.10%	6.80%
Agricultural business, including secured by farming [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	111,795
Agricultural business, including secured by farming [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	52,670
Agricultural business, including secured by farming [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	58,722
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	543,263	581,670	594,413
Percent of total loans	16.60%	18.00%	18.50%
One- to four-family real estate [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	337,369
One- to four-family real estate [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	180,047
One- to four-family real estate [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	23,846
One- to four-family real estate [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,001
Total consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	283,848	290,621	274,773
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	113,829	120,498	103,393
Percent of total loans	3.50%	3.70%	3.20%
Consumer [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	75,307
Consumer [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	32,942
Consumer [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,565
Consumer [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	15
Consumer secured by one- to four-family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	170,019	170,123	171,380
Percent of total loans	5.20%	5.30%	5.30%
Consumer secured by one- to four-family [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	112,130
Consumer secured by one- to four-family [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	44,049
Consumer secured by one- to four-family [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	13,195
Consumer secured by one- to four-family [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 645