SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Information about reportable segments
Net interest income	$ 66,881	$ 59,840
Provision for loan losses	1,341	623
Noninterest revenues	38,281	29,046
Amortization of intangible assets	1,442	919
Other operating expenses	66,227	55,029
Income before income taxes	36,152	32,315
Assets	8,615,901	7,576,039	$ 8,552,669
Goodwill	465,142	375,174	$ 463,252
Eliminations [Member]
Information about reportable segments
Net interest income	0	0
Provision for loan losses	0	0
Noninterest revenues	(566)	(464)
Amortization of intangible assets	0	0
Other operating expenses	(566)	(464)
Income before income taxes	0	0
Assets	(38,665)	(22,307)
Goodwill	0	0
Banking [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	66,798	59,785
Provision for loan losses	1,341	623
Noninterest revenues	15,313	13,524
Amortization of intangible assets	719	739
Other operating expenses	48,530	43,819
Income before income taxes	31,521	28,128
Assets	8,546,646	7,549,811
Goodwill	440,870	364,495
Employee Benefit Services [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	40	29
Provision for loan losses	0	0
Noninterest revenues	12,390	11,353
Amortization of intangible assets	116	133
Other operating expenses	9,447	8,451
Income before income taxes	2,867	2,798
Assets	38,535	32,206
Goodwill	8,019	8,019
All Other [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	43	26
Provision for loan losses	0	0
Noninterest revenues	11,144	4,633
Amortization of intangible assets	607	47
Other operating expenses	8,816	3,223
Income before income taxes	1,764	1,389
Assets	69,385	16,329
Goodwill	$ 16,253	$ 2,660