SEGMENT INFORMATION (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) segment	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment			3
SEGMENT INFORMATION
Net interest income (expense)	$ 37,805	$ 35,532	$ 111,334	$ 107,234
Provision (credit) for loan and lease losses	(3,647)	(1,722)	(13,713)	(1,043)
Other operating income	9,829	11,463	29,143	33,611
Other operating expense	(32,175)	(35,246)	(98,651)	(100,064)
Income tax (expenses) benefit	(6,900)	(5,241)	(20,603)	(14,636)
Net income	12,206	8,230	34,936	27,188
Investment securities	1,527,101		1,527,101		$ 1,467,305
Total Assets	5,021,833		5,021,833		4,852,987
Banking Operations
SEGMENT INFORMATION
Net income	12,737	9,600	40,455	23,101
Total Assets	3,180,630		3,180,630		3,052,952
Treasury
SEGMENT INFORMATION
Net income	622	(1,837)	(514)	1,271
Total Assets	1,759,211		1,759,211		1,715,760
All Others
SEGMENT INFORMATION
Net income	(1,153)	467	(5,005)	2,816
Total Assets	81,992		81,992		84,275
Intersegment elimination
SEGMENT INFORMATION
Net interest income (expense)	0	0	0	0
Intersegment elimination | Banking Operations
SEGMENT INFORMATION
Net interest income (expense)	11,176	11,619	32,826	23,775
Intersegment elimination | Treasury
SEGMENT INFORMATION
Net interest income (expense)	(7,477)	(11,231)	(24,242)	(24,950)
Intersegment elimination | All Others
SEGMENT INFORMATION
Net interest income (expense)	(3,699)	(388)	(8,584)	1,175
Operating segments
SEGMENT INFORMATION
Net interest income (expense)	37,805	35,532	111,334	107,234
Provision (credit) for loan and lease losses	3,647	1,722	13,713	1,043
Other operating income	9,829	11,463	29,143	33,611
Other operating expense	(32,175)	(35,246)	(98,651)	(100,064)
Administrative and overhead expense allocation	0	0	0	0
Income tax (expenses) benefit	(6,900)	(5,241)	(20,603)	(14,636)
Investment securities	1,527,101		1,527,101		1,467,305
Loans and leases (including loans held for sale)	3,111,249		3,111,249		2,941,881
Other	383,483		383,483		443,801
Operating segments | Banking Operations
SEGMENT INFORMATION
Net interest income (expense)	29,424	27,671	86,115	81,214
Provision (credit) for loan and lease losses	3,647	1,722	13,713	1,043
Other operating income	5,438	6,264	17,892	18,663
Other operating expense	(14,291)	(16,104)	(44,469)	(45,794)
Administrative and overhead expense allocation	(15,798)	(15,823)	(43,839)	(43,361)
Income tax (expenses) benefit	(6,859)	(5,749)	(21,783)	(12,439)
Investment securities	0		0		0
Loans and leases (including loans held for sale)	3,111,249		3,111,249		2,941,881
Other	69,381		69,381		111,071
Operating segments | Treasury
SEGMENT INFORMATION
Net interest income (expense)	8,381	7,861	25,219	26,020
Provision (credit) for loan and lease losses	0	0	0	0
Other operating income	734	1,453	439	3,290
Other operating expense	(436)	(509)	(1,407)	(1,598)
Administrative and overhead expense allocation	(245)	(268)	(799)	(807)
Income tax (expenses) benefit	(335)	857	276	(684)
Investment securities	1,527,101		1,527,101		1,467,305
Loans and leases (including loans held for sale)	0		0		0
Other	232,110		232,110		248,455
Operating segments | All Others
SEGMENT INFORMATION
Net interest income (expense)	0	0	0	0
Provision (credit) for loan and lease losses	0	0	0	0
Other operating income	3,657	3,746	10,812	11,658
Other operating expense	(17,448)	(18,633)	(52,775)	(52,672)
Administrative and overhead expense allocation	16,043	16,091	44,638	44,168
Income tax (expenses) benefit	294	$ (349)	904	$ (1,513)
Investment securities	0		0		0
Loans and leases (including loans held for sale)	0		0		0
Other	$ 81,992		$ 81,992		$ 84,275