SEGMENT INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Information about reportable segments
Net interest income	$ 59,840	$ 60,108
Provision for loan losses	623	1,000
Noninterest income	29,046	28,354
Amortization of intangible assets	919	1,141
Other operating expenses	55,029	54,780
Income before income taxes	32,315	31,541
Assets	7,576,039	7,397,228	7,489,440
Goodwill	375,174	375,174	375,174
Eliminations [Member]
Information about reportable segments
Net interest income	0	0
Provision for loan losses	0	0
Noninterest income	(464)	(474)
Amortization of intangible assets	0	0
Other operating expenses	(464)	(474)
Income before income taxes	0	0
Assets	(22,307)	(18,064)
Goodwill	0	0
Banking [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	59,785	60,063
Provision for loan losses	623	1,000
Noninterest income	13,524	13,444
Amortization of intangible assets	739	912
Other operating expenses	43,819	43,711
Income before income taxes	28,128	27,884
Assets	7,549,811	7,370,190
Goodwill	364,495	364,495
Employee Benefit Services [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	29	23
Provision for loan losses	0	0
Noninterest income	11,353	10,721
Amortization of intangible assets	133	172
Other operating expenses	8,451	8,297
Income before income taxes	2,798	2,275
Assets	32,206	30,719
Goodwill	8,019	8,019
Wealth Management [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	26	22
Provision for loan losses	0	0
Noninterest income	4,633	4,663
Amortization of intangible assets	47	57
Other operating expenses	3,223	3,246
Income before income taxes	1,389	1,382
Assets	16,329	14,383
Goodwill	$ 2,660	$ 2,660