SEGMENT INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Information about reportable segments
Net interest income	$ 61,170	$ 58,432	$ 121,279	$ 116,857
Provision for loan losses	1,900	1,321	2,900	2,714
Noninterest income	29,666	27,098	58,020	53,207
Amortization of intangible assets	1,101	1,140	2,242	2,319
Other operating expenses	54,063	53,236	108,844	106,609
Income before income taxes	33,772	29,833	65,313	58,422
Assets	7,461,343	7,020,716	7,461,343	7,020,716	7,095,864
Goodwill	375,174	369,703	375,174	369,703	374,991
Eliminations [Member]
Information about reportable segments
Net interest income	0	0	0	0
Provision for loan losses	0	0	0	0
Noninterest income	(418)	(416)	(880)	(852)
Amortization of intangible assets	0	0	0	0
Other operating expenses	(418)	(416)	(880)	(852)
Income before income taxes	0	0	0	0
Assets	(15,639)	(12,649)	(15,639)	(12,649)
Goodwill	0	0	0	0
Banking [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	61,124	58,380	121,188	116,753
Provision for loan losses	1,900	1,321	2,900	2,714
Noninterest income	14,778	13,655	28,223	26,295
Amortization of intangible assets	882	908	1,795	1,846
Other operating expenses	43,132	42,946	86,844	86,177
Income before income taxes	29,988	26,860	57,872	52,311
Assets	7,435,282	6,995,501	7,435,282	6,995,501
Goodwill	364,495	359,207	364,495	359,207
Employee Benefit Services Member [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	23	31	46	64
Provision for loan losses	0	0	0	0
Noninterest income	10,677	9,618	21,386	19,630
Amortization of intangible assets	171	175	342	349
Other operating expenses	8,198	7,610	16,482	15,208
Income before income taxes	2,331	1,864	4,608	4,137
Assets	27,818	25,662	27,818	25,662
Goodwill	8,019	7,836	8,019	7,836
Wealth Management [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	23	21	45	40
Provision for loan losses	0	0	0	0
Noninterest income	4,629	4,241	9,291	8,134
Amortization of intangible assets	48	57	105	124
Other operating expenses	3,151	3,096	6,398	6,076
Income before income taxes	1,453	1,109	2,833	1,974
Assets	13,882	12,202	13,882	12,202
Goodwill	$ 2,660	$ 2,660	$ 2,660	$ 2,660