SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Information 3 (Details) $ in Thousands		12 Months Ended
	Jul. 09, 2015	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Operating Segments
Number of reportable operating segments | item		1
Reclassifications
Reclassification effect		$ 0
Adoption of New Accounting Standards
Deferral period of new accounting standard after amendments	1 year
Income tax (benefit)		$ 12,936	$ 12,137	$ 10,233
Minimum
Equity
Stock dividends rate reported by transferring the par value of the stock issued from retained earnings to common stock (as a percent)		20.00%
Maximum
Equity
Stock dividends rate reported by transferring the fair value, as of the ex-dividend date, of the stock issued from retained earnings to common stock and additional paid-in capital (as a percent)		20.00%
Core deposit intangibles
Goodwill and Other Intangible Assets
Estimated useful lives of other intangible assets		10 years
Other customer relationship intangibles
Goodwill and Other Intangible Assets
Estimated useful lives of other intangible assets		10 years
Accounting Standards Update 2018-02 | Proforma Adjustment
Adoption of New Accounting Standards
Tax cuts and jobs act of 2017, Reclassification from AOCI to Retained Earnings		$ 905
Stock options | Accounting Standards Update 2016-09
Adoption of New Accounting Standards
Income tax (benefit)		(232)
Restricted stock | Accounting Standards Update 2016-09
Adoption of New Accounting Standards
Income tax (benefit)		$ (177)