SBM ACQUISITION - NARRATIVE (Details) - USD ($)		3 Months Ended		9 Months Ended
	Oct. 16, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 14, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill, Period Increase (Decrease)		$ 960,000
Assets		3,903,966,000		$ 3,903,966,000			$ 3,709,344,000
Loans and Leases Receivable, Net Amount		2,568,719,000		2,568,719,000			2,469,040,000
Deposits		$ 2,889,225,000		$ 2,889,225,000			$ 2,726,379,000
Common stock, outstanding (shares)		15,434,856		15,434,856			15,330,717
Merger and acquisition costs		$ 45,000	$ 766,000	$ 866,000	$ 1,629,000
Business Combination Provisional Information Initial Accounting Incomplete Adjustment Impact on Earnings				0
Share Price						$ 31.75
SBM Financial, Inc.
Business Acquisition [Line Items]
Goodwill, Period Increase (Decrease)				(960,000)
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Assets				137,000
Consideration transferred	$ 136,676,000
Cash	26,125,000
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	$ 108,561,000
Business Combination Provisional Information Initial Accounting Incomplete Adjustment Other Assets				157,000
Business Combination Provisional Information Initial Accounting Incomplete Adjustment Deferred Tax Asset				$ 666,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	4,124,643
Share Price	$ 26.32
Nonqualified Stock Options [Member] | SBM Financial, Inc.
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	$ 1,990,000