DEPOSITS AND RETAIL REPURCHASE AGREEMENTS (Geographic Concentration of Deposits) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Deposit Liabilities [Line Items]
Total deposits	$ 4,297,145	$ 3,898,950
Percent of total deposits	100.00%	100.00%
Washington [Member]
Deposit Liabilities [Line Items]
Total deposits	$ 2,858,101
Percent of total deposits	66.50%
Oregon [Member]
Deposit Liabilities [Line Items]
Total deposits	$ 1,195,413
Percent of total deposits	27.80%
Idaho [Member]
Deposit Liabilities [Line Items]
Total deposits	$ 243,631
Percent of total deposits	5.70%