LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Loans by Geographic Type) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 3,213,523	$ 3,296,338	$ 3,225,246
Percent of total loans	100.00%	100.00%	100.00%
Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,161,333
Percent of total loans	67.30%
Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	671,391
Percent of total loans	20.90%
Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	283,917
Percent of total loans	8.80%
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	96,882
Percent of total loans	3.00%
Commerical real estate - owner-occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	477,871	469,806	474,863
Percent of total loans	14.90%	14.20%	14.70%
Commerical real estate - owner-occupied [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	360,406
Commerical real estate - owner-occupied [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	53,929
Commerical real estate - owner-occupied [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	58,799
Commerical real estate - owner-occupied [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,737
Commerical real estate - investment properties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	604,265	621,622	586,652
Percent of total loans	18.80%	18.90%	18.20%
Commerical real estate - investment properties [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	471,723
Commerical real estate - investment properties [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	81,874
Commerical real estate - investment properties [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	44,187
Commerical real estate - investment properties [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,481
Multifamily real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	138,716	139,710	134,146
Percent of total loans	4.30%	4.20%	4.20%
Multifamily real estate [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	117,769
Multifamily real estate [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	13,190
Multifamily real estate [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	7,436
Multifamily real estate [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	321
Commercial construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	28,598	42,391	38,124
Percent of total loans	0.90%	1.30%	1.20%
Commercial construction [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	20,030
Commercial construction [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,998
Commercial construction [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,159
Commercial construction [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,411
Multifamily construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	14,502	19,436	16,335
Percent of total loans	0.50%	0.60%	0.50%
Multifamily construction [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,498
Multifamily construction [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,004
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	163,521	144,177	145,776
Percent of total loans	5.10%	4.40%	4.50%
One-to four-family construction [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	88,350
One-to four-family construction [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	73,375
One-to four-family construction [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,796
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	79,932	97,491	96,875
Percent of total loans	2.50%	3.00%	3.00%
Land and land development - residential [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	39,181
Land and land development - residential [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	38,781
Land and land development - residential [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,970
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	14,242	15,197	19,173
Percent of total loans	0.40%	0.50%	0.60%
Land and land development - commercial [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,205
Land and land development - commercial [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,107
Land and land development - commercial [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,930
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	603,606	601,440	580,876
Percent of total loans	18.80%	18.20%	18.00%
Commercial business [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	387,598
Commercial business [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	75,609
Commercial business [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	59,461
Commercial business [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	80,938
Agricultural business, including secured by farming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	219,084	218,171	211,571
Percent of total loans	6.80%	6.60%	6.60%
Agricultural business, including secured by farming [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	109,099
Agricultural business, including secured by farming [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	45,418
Agricultural business, including secured by farming [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	64,567
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	594,413	642,501	639,909
Percent of total loans	18.50%	19.50%	19.80%
One- to four-family real estate [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	365,510
One- to four-family real estate [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	201,898
One- to four-family real estate [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	24,542
One- to four-family real estate [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,463
Total consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	274,773	284,396	280,946
Percent of total loans	8.50%	8.60%	8.70%
Total consumer [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	182,964
Total consumer [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	74,208
Total consumer [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	17,070
Total consumer [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	531
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	103,393	103,347	98,794
Percent of total loans	3.20%	3.10%	3.10%
Consumer [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	66,837
Consumer [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	31,154
Consumer [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,402
Consumer [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
Consumer secured by one- to four-family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	171,380	181,049	182,152
Percent of total loans	5.30%	5.50%	5.60%
Consumer secured by one- to four-family [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	116,127
Consumer secured by one- to four-family [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	43,054
Consumer secured by one- to four-family [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	11,668
Consumer secured by one- to four-family [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 531