SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Selected Quarterly Financial Information [Abstract]
Interest income	$ 101,007	$ 97,849	$ 97,321	$ 95,301	$ 96,495	$ 54,793	$ 54,076	$ 49,069	$ 49,251	$ 49,764	$ 46,540	$ 45,106	$ 391,477	$ 254,433	$ 190,661
Interest expense	3,836	4,141	4,173	4,258	4,396	2,605	2,619	2,533	2,590	2,700	2,732	2,767	16,408	12,154	10,789
Interest-bearing deposits	97,171	93,708	93,148	91,043	92,099	52,188	51,457	46,536	46,661	47,064	43,808	42,339	375,069	242,279	179,872
Provision for loan losses	2,030	2,000	2,000	0	0	0	0	0	0	0	0	0	6,030	0	0
Net interest income	95,141	91,708	91,148	91,043	92,099	52,188	51,457	46,536	46,661	47,064	43,808	42,339	369,039	242,279	179,872
Non-interest income	19,463	23,512	20,537	19,959	18,356	14,098	16,141	13,696	12,113	13,536	20,310	9,032	83,470	62,292	54,991
Other operating expenses	79,857	79,092	79,887	84,034	100,254	46,697	47,734	41,914	41,230	38,495	38,435	35,581	322,869	236,600	153,741
Income before provision for income taxes	34,747	36,128	31,798	26,968	10,201	19,589	19,864	18,318	17,544	22,105	25,683	15,790	129,640	67,971	81,122
PROVISION FOR INCOME TAXES	11,943	12,277	10,841	9,194	3,308	6,642	6,615	6,184	5,831	7,284	8,696	5,241	44,255	22,749	27,052
NET INCOME	$ 22,804	$ 23,851	$ 20,957	$ 17,774	$ 6,893	$ 12,947	$ 13,249	$ 12,134	$ 11,713	$ 14,821	$ 16,987	$ 10,549	$ 85,385	$ 45,222	$ 54,070
Basic earnings (loss) per share (in dollars per share)	$ 0.69	$ 0.70	$ 0.62	$ 0.52	$ 0.20	$ 0.62	$ 0.64	$ 0.61	$ 0.60	$ 0.76	$ 0.88	$ 0.55	$ 2.52	$ 1.90	$ 2.79
Diluted earnings (loss) per share (in dollars per share)	0.69	0.70	0.61	0.52	0.20	0.62	0.64	0.61	0.60	0.76	0.88	0.54	2.52	1.89	2.79
Cumulative dividends declared per common share (in dollars per share)	$ 0.23	$ 0.23	$ 0.21	$ 0.21	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.88	$ 0.72	$ 0.72