SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Information about reportable segments
Net interest income	$ 61,228	$ 61,170	$ 121,068	$ 121,279
Provision for loan losses	591	1,900	1,214	2,900
Noninterest revenues	29,719	29,666	58,765	58,020
Amortization of intangible assets	880	1,101	1,799	2,242
Other operating expenses	55,168	54,063	110,197	108,844
Income before income taxes	34,308	33,772	66,623	65,313
Assets	7,908,771	7,461,343	7,908,771	7,461,343	$ 7,489,440
Goodwill	375,174	375,174	375,174	375,174	$ 375,174
Eliminations [Member]
Information about reportable segments
Net interest income	0	0	0	0
Provision for loan losses	0	0	0	0
Noninterest revenues	(472)	(418)	(936)	(880)
Amortization of intangible assets	0	0	0	0
Other operating expenses	(472)	(418)	(936)	(880)
Income before income taxes	0	0	0	0
Assets	(24,783)	(15,639)	(24,783)	(15,639)
Goodwill	0	0	0	0
Banking [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	61,165	61,124	120,948	121,188
Provision for loan losses	591	1,900	1,214	2,900
Noninterest revenues	14,009	14,778	27,534	28,223
Amortization of intangible assets	709	882	1,448	1,795
Other operating expenses	43,393	43,132	87,212	86,844
Income before income taxes	30,481	29,988	58,608	57,872
Assets	7,882,898	7,435,282	7,882,898	7,435,282
Goodwill	364,495	364,495	364,495	364,495
Employee Benefit Services [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	35	23	65	46
Provision for loan losses	0	0	0	0
Noninterest revenues	11,606	10,677	22,959	21,386
Amortization of intangible assets	133	171	266	342
Other operating expenses	8,957	8,198	17,408	16,482
Income before income taxes	2,551	2,331	5,350	4,608
Assets	33,609	27,818	33,609	27,818
Goodwill	8,019	8,019	8,019	8,019
Wealth Management [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	28	23	55	45
Provision for loan losses	0	0	0	0
Noninterest revenues	4,576	4,629	9,208	9,291
Amortization of intangible assets	38	48	85	105
Other operating expenses	3,290	3,151	6,513	6,398
Income before income taxes	1,276	1,453	2,665	2,833
Assets	17,047	13,882	17,047	13,882
Goodwill	$ 2,660	$ 2,660	$ 2,660	$ 2,660