SEGMENT INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Information about reportable segments [Abstract]
Net interest income	$ 238,094	$ 230,424	$ 209,413
Provision for loan losses	7,992	9,108	4,736
Noninterest income	102,180	99,246	89,222
Amortization of intangible assets	4,469	4,607	4,381
Other operating expenses	216,786	207,150	185,991
Income before income taxes	111,027	108,805	103,527
Assets	7,095,864	7,496,800	6,488,275
Goodwill	374,991	369,703	345,050
Eliminations [Member]
Information about reportable segments [Abstract]
Net interest income	0	0	0
Provision for loan losses	0	0	0
Noninterest income	(1,649)	(1,506)	(1,322)
Amortization of intangible assets	0	0	0
Other operating expenses	(1,649)	(1,506)	(1,322)
Income before income taxes	0	0	0
Assets	(16,231)	(18,334)	(11,976)
Goodwill	0	0	0
Banking [Member]
Information about reportable segments [Abstract]
Net interest income	237,915	230,251	209,302
Provision for loan losses	7,992	9,108	4,736
Noninterest income	48,030	50,422	46,921
Amortization of intangible assets	3,569	3,548	3,393
Other operating expenses	175,139	167,332	152,468
Income before income taxes	99,245	100,685	95,626
Assets	7,070,866	7,472,628	6,461,694
Goodwill	364,495	359,207	334,554
Employee Benefit Services [Member]
Information about reportable segments [Abstract]
Net interest income	101	104	60
Provision for loan losses	0	0	0
Noninterest income	39,534	36,781	32,395
Amortization of intangible assets	662	779	752
Other operating expenses	31,049	30,617	25,622
Income before income taxes	7,924	5,489	6,081
Assets	27,970	30,405	27,446
Goodwill	7,836	7,836	7,836
Wealth Management [Member]
Information about reportable segments [Abstract]
Net interest income	78	69	51
Provision for loan losses	0	0	0
Noninterest income	16,265	13,549	11,228
Amortization of intangible assets	238	280	236
Other operating expenses	12,247	10,707	9,223
Income before income taxes	3,858	2,631	1,820
Assets	13,259	12,101	11,111
Goodwill	$ 2,660	$ 2,660	$ 2,660