SUMMARY OF 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
Consolidated quarterly financial data
Interest income	$ 56,349	$ 53,725	$ 47,821	$ 60,883	$ 45,903	$ 43,934	$ 40,140	$ 44,015	$ 218,778	$ 173,992	$ 142,432
Interest expense	5,711	5,418	4,684	4,445	4,258	4,536	4,563	4,581	20,258	17,938	18,462
NET INTEREST INCOME	50,638	48,307	43,137	56,438	41,645	39,398	35,577	39,434	198,520	156,054	123,970
Provision for loan and lease losses	6,071	4,221	5,061	12,351	5,004	2,489	1,814	5,186	27,704	14,493	5,396
NET INTEREST INCOME AFTER PROVISION FOR LOAN AND LEASE LOSSES	44,567	44,086	38,076	44,087	36,641	36,909	33,763	34,248	170,816	141,561	118,574
Non interest income	10,190	10,374	12,927	24,923	10,485	11,301	10,802	24,921	58,414	57,509	47,994
Non interest expenses	38,145	38,026	35,734	38,939	32,166	33,534	31,866	32,541	150,844	130,107	113,324
INCOME BEFORE INCOME TAX EXPENSE	16,612	16,434	15,269	30,071	14,960	14,676	12,699	26,628	78,386	68,963	53,244
Income tax expense (benefit)	11,774	5,728	5,198	10,054	4,960	4,848	4,359	8,893	32,754	23,060	18,078
NET INCOME	$ 4,838	$ 10,706	$ 10,071	$ 20,017	$ 10,000	$ 9,828	$ 8,340	$ 17,735	$ 45,632	$ 45,903	$ 35,166
Class A Common Stock
Basic earnings per share:
Basic earnings per share (in dollars per share)	$ 0.23	$ 0.51	$ 0.48	$ 0.97	$ 0.48	$ 0.47	$ 0.40	$ 0.86	$ 2.21	$ 2.22	$ 1.70
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	0.23	0.51	0.48	0.96	0.48	0.47	0.40	0.85	2.20	2.22	1.70
Dividends declared per common share:
Dividend declared common stock, per share (in dollars per share)	0.220	0.220	0.220	0.209	0.209	0.209	0.209	0.198	0.869	0.825	0.781
Class B Common Stock
Basic earnings per share:
Basic earnings per share (in dollars per share)	0.21	0.47	0.44	0.88	0.44	0.43	0.37	0.78	2.01	2.02	1.55
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	0.21	0.47	0.44	0.88	0.44	0.43	0.37	0.77	2.00	2.01	1.54
Dividends declared per common share:
Dividend declared common stock, per share (in dollars per share)	$ 0.200	$ 0.200	$ 0.200	$ 0.190	$ 0.190	$ 0.190	$ 0.190	$ 0.180	$ 0.790	$ 0.750	$ 0.710