LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Land and Land Development by State) (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%
Land and land development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	86,807
Percent of total loans	100.00%
Land and land development [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	51,196
Percent of total loans	59.00%
Land and land development [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	32,352
Percent of total loans	37.30%
Land and land development [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,259
Percent of total loans	3.70%
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] | Acquisition and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	28,119
Land and land development - residential [Member] | Acquisition and Development [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	17,094
Land and land development - residential [Member] | Acquisition and Development [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,901
Land and land development - residential [Member] | Acquisition and Development [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,124
Land and land development - residential [Member] | Improved Land and Lots [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	42,061
Land and land development - residential [Member] | Improved Land and Lots [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	23,201
Land and land development - residential [Member] | Improved Land and Lots [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	18,662
Land and land development - residential [Member] | Improved Land and Lots [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	198
Land and land development - residential [Member] | Unimproved Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,396
Land and land development - residential [Member] | Unimproved Land [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,986
Land and land development - residential [Member] | Unimproved Land [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	410
Land and land development - residential [Member] | Unimproved Land [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
Land and land development - commercial and industrial [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 and industrial [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,915
Land and land development - commercial and industrial [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,379
Land and land development - commercial and industrial [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,937
Land and land development - commercial and industrial [Member] | Acquisition and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	484
Land and land development - commercial and industrial [Member] | Acquisition and Development [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
Land and land development - commercial and industrial [Member] | Acquisition and Development [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
Land and land development - commercial and industrial [Member] | Acquisition and Development [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	484
Land and land development - commercial and industrial [Member] | Improved Land and Lots [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,245
Land and land development - commercial and industrial [Member] | Improved Land and Lots [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,213
Land and land development - commercial and industrial [Member] | Improved Land and Lots [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	525
Land and land development - commercial and industrial [Member] | Improved Land and Lots [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	507
Land and land development - commercial and industrial [Member] | Unimproved Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,502
Land and land development - commercial and industrial [Member] | Unimproved Land [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,702
Land and land development - commercial and industrial [Member] | Unimproved Land [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,854
Land and land development - commercial and industrial [Member] | Unimproved Land [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 946