SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	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, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Selected Quarterly Financial Information [Abstract]
Interest income	$ 96,495	$ 54,793	$ 54,076	$ 49,069	$ 49,251	$ 49,764	$ 46,540	$ 45,106	$ 44,596	$ 45,037	$ 45,571	$ 44,508	$ 254,433	$ 190,661	$ 179,712
Interest expense	4,396	2,605	2,619	2,533	2,590	2,700	2,732	2,767	2,989	3,144	3,323	3,540	12,154	10,789	12,996
Net interest income before provision for loan losses	92,099	52,188	51,457	46,536	46,661	47,064	43,808	42,339	41,607	41,893	42,248	40,968	242,279	179,872	166,716
Provision for loan losses	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Net interest income	92,099	52,188	51,457	46,536	46,661	47,064	43,808	42,339	41,607	41,893	42,248	40,968	242,279	179,872	166,716
Non-interest income	18,356	14,098	16,141	13,696	12,113	13,536	20,310	9,032	13,029	10,592	10,953	10,088	62,292	54,991	44,662
Other operating expenses	100,254	46,697	47,734	41,914	41,230	38,495	38,435	35,581	36,929	34,490	35,457	34,099	236,600	153,741	140,975
Income before provision for income taxes	10,201	19,589	19,864	18,318	17,544	22,105	25,683	15,790	17,707	17,995	17,744	16,957	67,971	81,122	70,403
PROVISION FOR INCOME TAXES	3,308	6,642	6,615	6,184	5,831	7,284	8,696	5,241	6,281	6,459	6,076	5,373	22,749	27,052	24,189
NET INCOME	$ 6,893	$ 12,947	$ 13,249	$ 12,134	$ 11,713	$ 14,821	$ 16,987	$ 10,549	$ 11,426	$ 11,536	$ 11,668	$ 11,584	$ 45,222	$ 54,070	$ 46,214
Basic earnings (loss) per share (in dollars per share)	$ 0.20	$ 0.62	$ 0.64	$ 0.61	$ 0.60	$ 0.76	$ 0.88	$ 0.55	$ 0.59	$ 0.60	$ 0.60	$ 0.60	$ 1.90	$ 2.79	$ 2.39
Diluted earnings (loss) per share (in dollars per share)	0.20	0.62	0.64	0.61	0.60	0.76	0.88	0.54	0.59	0.59	0.60	0.60	1.89	2.79	2.38
Cumulative dividends declared per common share (in dollars per share)	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.15	$ 0.15	$ 0.12	$ 0.12	$ 0.72	$ 0.72	$ 0.54