QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended											12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016		Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
QUARTERLY FINANCIAL DATA (UNAUDITED)
Interest income	$ 39,960		$ 38,438	$ 36,234	$ 35,217	$ 34,615		$ 34,761	$ 34,733	$ 33,607		$ 149,849	$ 137,716	$ 106,240
Interest expense	6,399		6,093	5,441	4,756	4,450		4,077	4,143	4,175		22,689	16,845	10,129
Net interest income	33,561		32,345	30,793	30,461	30,165		30,684	30,590	29,432		127,160	120,871	96,111
Provision for loan losses	10,400	[1]	1,900	950	800	1,400		2,000	900	1,250		14,050	5,550	4,000
Net interest income after provision for loan losses	23,161		30,445	29,843	29,661	28,765		28,684	29,690	28,182		113,110	115,321	92,111
Non-interest income	4,499		4,972	4,509	4,122	3,748		4,034	4,269	3,995		18,102	16,046	12,668
Non-interest expenses	29,154	[2]	21,271	21,006	20,296	18,529	[3]	19,204	20,441	18,907	[4]	91,727	77,081	72,890
Income before income taxes	(1,494)		14,146	13,346	13,487	13,984		13,514	13,518	13,270		39,485	54,286	31,889
Income tax expense	5,422	[5]	4,703	4,505	4,316	4,824		4,663	4,664	4,644		18,946	18,795	10,778
Net income	$ (6,916)		$ 9,443	$ 8,841	$ 9,171	$ 9,160		$ 8,851	$ 8,854	$ 8,626		$ 20,539	$ 35,491	$ 21,111
Basic earnings (loss) per share (in dollars per share)	$ (0.35)		$ 0.48	$ 0.45	$ 0.47	$ 0.50		$ 0.50	$ 0.51	$ 0.49		$ 1.04	$ 2.01	$ 1.43
Diluted earnings (loss) per share (in dollars per share)	$ (0.35)		$ 0.48	$ 0.45	$ 0.47	$ 0.50		$ 0.50	$ 0.50	$ 0.49		$ 1.04	$ 2.00	$ 1.43

[1] 2017 amount includes net charge-offs primarily from loans and specific reserves associated with two relationships of $8.0 million.

[2] 2017 amount includes restructuring costs associated with branch restructuring and charter conversion of $8.0 million.

[3] 2016 amount includes reversal of costs associated with the CNB and FNBNY acquisitions of $0.7 million.

[4] 2016 amount includes reversal of costs associated with the CNB and FNBNY acquisitions of $0.3 million.

[5] 2017 amount includes a charge to write-down deferred tax assets due to the enactment of the Tax Act of $7.6 million.