LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Land and Land Development by State) (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%
Land and land development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	90,923
Percent of total loans	100.00%
Land and land development [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	54,588
Percent of total loans	60.00%
Land and land development [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	32,657
Percent of total loans	35.90%
Land and land development [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,678
Percent of total loans	4.10%
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] | Acquisition and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	22,576
Land and land development - residential [Member] | Acquisition and Development [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,982
Land and land development - residential [Member] | Acquisition and Development [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	12,071
Land and land development - residential [Member] | Acquisition and Development [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,523
Land and land development - residential [Member] | Improved Land and Lots [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	46,759
Land and land development - residential [Member] | Improved Land and Lots [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	29,463
Land and land development - residential [Member] | Improved Land and Lots [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	17,093
Land and land development - residential [Member] | Improved Land and Lots [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	203
Land and land development - residential [Member] | Unimproved Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,111
Land and land development - residential [Member] | Unimproved Land [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,661
Land and land development - residential [Member] | Unimproved Land [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	450
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	12,477	13,982	12,044
Percent of total loans	0.40%	0.40%	0.40%
Land and land development - commercial and industrial [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	7,482
Land and land development - commercial and industrial [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,043
Land and land development - commercial and industrial [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,952
Land and land development - commercial and industrial [Member] | Acquisition and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	482
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	482
Land and land development - commercial and industrial [Member] | Improved Land and Lots [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,820
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	4,143
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	136
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	541
Land and land development - commercial and industrial [Member] | Unimproved Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	7,175
Land and land development - commercial and industrial [Member] | Unimproved Land [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,339
Land and land development - commercial and industrial [Member] | Unimproved Land [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,907
Land and land development - commercial and industrial [Member] | Unimproved Land [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 929