GOODWILL AND INTANGIBLE ASSETS - Acquired Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Acquired intangible assets
Accumulated amortization	$ (30,921)	$ (28,910)
Purchased intangibles, net	13,901	7,419
Aggregate amortization expense	2,011	1,342	$ 1,640
Estimated amortization expense
2018	2,240
2019	1,902
2020	1,643
2021	1,417
2022	1,167
Thereafter	5,532
Core deposit intangibles
Acquired intangible assets
Purchased intangibles, gross	40,398	34,135
Other customer relationship intangibles
Acquired intangible assets
Purchased intangibles, gross	$ 4,424	$ 2,194