LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Land and Land Development by State) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 4,114,818	$ 3,833,820
Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,403,473
Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,091,398
Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	311,940
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	308,007
Land and land development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	116,104
Percent of total loans	100.00%
Land and land development [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	59,662
Percent of total loans	51.40%
Land and land development [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	51,900
Percent of total loans	44.70%
Land and land development [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,867
Percent of total loans	3.30%
Land and land development [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	675
Percent of total loans	0.60%
Land and land development - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	98,930	102,435
Land and land development - residential [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	53,476
Land and land development - residential [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	43,737
Land and land development - residential [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,042
Land and land development - residential [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	675
Land and land development - residential [Member] | Acquisition and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	55,866
Land and land development - residential [Member] | Acquisition and Development [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	29,923
Land and land development - residential [Member] | Acquisition and Development [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	25,033
Land and land development - residential [Member] | Acquisition and Development [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	910
Land and land development - residential [Member] | Acquisition and Development [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
Land and land development - residential [Member] | Improved Land and Lots [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	36,441
Land and land development - residential [Member] | Improved Land and Lots [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	20,511
Land and land development - residential [Member] | Improved Land and Lots [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	15,114
Land and land development - residential [Member] | Improved Land and Lots [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	141
Land and land development - residential [Member] | Improved Land and Lots [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	675
Land and land development - residential [Member] | Unimproved Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,623
Land and land development - residential [Member] | Unimproved Land [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,034
Land and land development - residential [Member] | Unimproved Land [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,589
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 - residential [Member] | Unimproved Land [Member] | Other [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	17,174	11,152
Land and land development - commercial and industrial [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,194
Land and land development - commercial and industrial [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,164
Land and land development - commercial and industrial [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,816
Land and land development - commercial and industrial [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
Land and land development - commercial and industrial [Member] | Improved Land and Lots [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	11,060
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	3,414
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	5,865
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	1,781
Land and land development - commercial and industrial [Member] | Improved Land and Lots [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	0
Land and land development - commercial and industrial [Member] | Unimproved Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,114
Land and land development - commercial and industrial [Member] | Unimproved Land [Member] | Washington [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,780
Land and land development - commercial and industrial [Member] | Unimproved Land [Member] | Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,299
Land and land development - commercial and industrial [Member] | Unimproved Land [Member] | Idaho [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,035
Land and land development - commercial and industrial [Member] | Unimproved Land [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 0