SEGMENT INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Information about reportable segments
Net interest income	$ 61,394	$ 60,601	$ 182,672	$ 177,458
Provision for loan losses	1,747	2,093	4,647	4,807
Noninterest income	31,072	27,594	89,092	80,801
Amortization of intangible assets	1,051	1,089	3,293	3,408
Other operating expenses	57,760	53,955	166,603	160,564
Income before income taxes	31,908	31,058	97,221	89,480
Assets	7,502,643	7,302,017	7,502,643	7,302,017	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	(486)	(357)	(1,365)	(1,210)
Amortization of intangible assets	0	0	0	0
Other operating expenses	(486)	(357)	(1,365)	(1,210)
Income before income taxes	0	0	0	0
Assets	(17,957)	(14,519)	(17,957)	(14,519)
Goodwill	0	0	0	0
Banking [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	61,350	60,566	182,537	177,319
Provision for loan losses	1,747	2,093	4,647	4,807
Noninterest income	15,700	14,372	43,922	40,667
Amortization of intangible assets	850	875	2,644	2,720
Other operating expenses	46,837	43,497	133,680	129,674
Income before income taxes	27,616	28,473	85,488	80,785
Assets	7,476,030	7,276,673	7,476,030	7,276,673
Goodwill	364,495	359,207	364,495	359,207
Employee Benefit Services [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	21	16	67	81
Provision for loan losses	0	0	0	0
Noninterest income	11,049	9,619	32,434	29,249
Amortization of intangible assets	153	157	496	507
Other operating expenses	8,140	7,810	24,622	23,019
Income before income taxes	2,777	1,668	7,383	5,804
Assets	29,605	27,228	29,605	27,228
Goodwill	8,019	7,836	8,019	7,836
Wealth Management [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	23	19	68	58
Provision for loan losses	0	0	0	0
Noninterest income	4,809	3,960	14,101	12,095
Amortization of intangible assets	48	57	153	181
Other operating expenses	3,269	3,005	9,666	9,081
Income before income taxes	1,515	917	4,350	2,891
Assets	14,965	12,635	14,965	12,635
Goodwill	$ 2,660	$ 2,660	$ 2,660	$ 2,660