ALLOWANCE FOR LOAN AND LEASE LOSSES - Changes in the Allowance for Loan and Lease Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2013
Allowance for loan and lease losses:
Balance at beginning of period	$ 42,128	$ 42,027	$ 42,820	$ 43,829	$ 43,829
Provision for loan and lease losses	1,382	1,093	6,114	2,281
Gross charge-offs	2,385	1,816	9,200	6,427
Recoveries	1,194	1,150	2,585	2,771
Total net charge-offs			6,615
Balance at end of period	42,319	42,454	42,319	42,454	42,820
Ending allowance on loans individually evaluated for impairment	1,653		1,653		5,053
Ending allowance on loans collectively evaluated for impairment	51,679		51,679		47,805
Loans and Leases:
Ending balance of loans individually evaluated for impairment	33,042		33,042		35,632
Ending balance of loans collectively evaluated for impairment	5,183,021		5,183,021		4,741,603
Loans and Leases Receivable, Net of Deferred Income	5,216,063		5,216,063		4,777,235
Loans and Leases Receivable Covered Loans	237,825		237,825		302,014
Loans and Leases Receivable, Gross, Carrying Amount, Covered and Noncovered	5,216,063		5,216,063		4,777,235
Loans and Leases Receivable, Allowance, Covered	11,013	11,535	11,013	11,535	10,038	$ 10,748	$ 12,425	$ 18,901
Loans charged-off	1,577	$ 3,053	5,078	13,778	18,096
Allowance for Loan and Lease Losses Write-offs, Net, Covered and Noncovered			7,303		11,400
Non Covered Loans
Allowance for loan and lease losses:
Balance at beginning of period			42,820	43,829	43,829
Provision for loan and lease losses			6,114		3,369
Gross charge-offs			9,200		7,877
Recoveries			2,585		3,499
Total net charge-offs					4,378
Balance at end of period					42,820
Ending allowance on loans individually evaluated for impairment	1,653		1,653		5,053
Ending allowance on loans collectively evaluated for impairment	40,666		40,666		37,767
Loans and Leases:
Ending balance of loans individually evaluated for impairment	33,042		33,042		35,632
Ending balance of loans collectively evaluated for impairment	4,945,196		4,945,196		4,439,589
Loans and Leases Receivable, Net of Deferred Income	4,978,238		4,978,238		4,475,221
Covered Loans
Allowance for loan and lease losses:
Ending allowance on loans individually evaluated for impairment	0		0		0
Ending allowance on loans collectively evaluated for impairment	11,013		11,013		10,038
Loans and Leases:
Ending balance of loans individually evaluated for impairment	0		0		0
Ending balance of loans collectively evaluated for impairment	237,825		237,825		302,014
Loans and Leases Receivable, Allowance, Covered	11,013		11,013
Commercial
Allowance for loan and lease losses:
Balance at beginning of period			11,259	10,568	10,568
Total net charge-offs			1,942
Balance at end of period	14,351		14,351		11,259
Ending allowance on loans individually evaluated for impairment	478		478		739
Commercial | Non Covered Loans
Allowance for loan and lease losses:
Balance at beginning of period			11,259
Provision for loan and lease losses			5,034		871
Gross charge-offs			2,528		1,440
Recoveries			586		1,260
Total net charge-offs					180
Balance at end of period					11,259
Ending allowance on loans individually evaluated for impairment	478		478		739
Ending allowance on loans collectively evaluated for impairment	13,873		13,873		10,520
Loans and Leases:
Ending balance of loans individually evaluated for impairment	7,651		7,651		6,122
Ending balance of loans collectively evaluated for impairment	1,620,696		1,620,696		1,291,190
Loans and Leases Receivable, Net of Deferred Income	1,628,347		1,628,347		1,297,312
Real estate - construction
Allowance for loan and lease losses:
Balance at beginning of period			1,045	824	824
Total net charge-offs			45
Balance at end of period	1,540		1,540		1,045
Ending allowance on loans individually evaluated for impairment	0		0		0
Real estate - construction | Non Covered Loans
Allowance for loan and lease losses:
Balance at beginning of period			1,045
Provision for loan and lease losses			540		221
Gross charge-offs			84		0
Recoveries			39		0
Total net charge-offs					0
Balance at end of period					1,045
Ending allowance on loans individually evaluated for impairment	0		0		0
Ending allowance on loans collectively evaluated for impairment	1,540		1,540		1,045
Loans and Leases:
Ending balance of loans individually evaluated for impairment	0		0		0
Ending balance of loans collectively evaluated for impairment	275,430		275,430		196,272
Loans and Leases Receivable, Net of Deferred Income	275,430		275,430		196,272
Real estate - commercial
Allowance for loan and lease losses:
Balance at beginning of period			20,668	20,478	20,478
Total net charge-offs			2,687
Balance at end of period	15,699		15,699		20,668
Ending allowance on loans individually evaluated for impairment	938		938		4,002
Real estate - commercial | Non Covered Loans
Allowance for loan and lease losses:
Balance at beginning of period			20,668
Provision for loan and lease losses			(2,282)		1,325
Gross charge-offs			3,664		2,329
Recoveries			977		1,194
Total net charge-offs					1,135
Balance at end of period					20,668
Ending allowance on loans individually evaluated for impairment	938		938		4,002
Ending allowance on loans collectively evaluated for impairment	14,761		14,761		16,666
Loans and Leases:
Ending balance of loans individually evaluated for impairment	22,287		22,287		25,938
Ending balance of loans collectively evaluated for impairment	2,019,783		2,019,783		1,948,757
Loans and Leases Receivable, Net of Deferred Income	2,042,070		2,042,070		1,974,695
Real estate - residential
Allowance for loan and lease losses:
Balance at beginning of period			2,828	3,379	3,379
Total net charge-offs			491
Balance at end of period	3,661		3,661		2,828
Ending allowance on loans individually evaluated for impairment	235		235		310
Real estate - residential | Non Covered Loans
Allowance for loan and lease losses:
Balance at beginning of period			2,828
Provision for loan and lease losses			1,324		181
Gross charge-offs			665		922
Recoveries			174		190
Total net charge-offs					732
Balance at end of period					2,828
Ending allowance on loans individually evaluated for impairment	235		235		310
Ending allowance on loans collectively evaluated for impairment	3,426		3,426		2,518
Loans and Leases:
Ending balance of loans individually evaluated for impairment	2,742		2,742		2,963
Ending balance of loans collectively evaluated for impairment	444,132		444,132		429,712
Loans and Leases Receivable, Net of Deferred Income	446,874		446,874		432,675
Installment
Allowance for loan and lease losses:
Balance at beginning of period			323	365	365
Total net charge-offs			104
Balance at end of period	296		296		323
Ending allowance on loans individually evaluated for impairment	0		0		0
Installment | Non Covered Loans
Allowance for loan and lease losses:
Balance at beginning of period			323
Provision for loan and lease losses			77		23
Gross charge-offs			267		283
Recoveries			163		218
Total net charge-offs					65
Balance at end of period					323
Ending allowance on loans individually evaluated for impairment	0		0		0
Ending allowance on loans collectively evaluated for impairment	296		296		323
Loans and Leases:
Ending balance of loans individually evaluated for impairment	0		0		0
Ending balance of loans collectively evaluated for impairment	37,609		37,609		44,269
Loans and Leases Receivable, Net of Deferred Income	37,609		37,609		44,269
Home equity
Allowance for loan and lease losses:
Balance at beginning of period			4,260	5,209	5,209
Total net charge-offs			707
Balance at end of period	4,458		4,458		4,260
Home equity | Non Covered Loans
Allowance for loan and lease losses:
Balance at beginning of period			4,260
Provision for loan and lease losses			905		565
Gross charge-offs			1,185		1,745
Recoveries			478		231
Total net charge-offs					1,514
Balance at end of period					4,260
Ending allowance on loans individually evaluated for impairment	2		2		2
Ending allowance on loans collectively evaluated for impairment	4,456		4,456		4,258
Loans and Leases:
Ending balance of loans individually evaluated for impairment	362		362		609
Ending balance of loans collectively evaluated for impairment	427,038		427,038		415,420
Loans and Leases Receivable, Net of Deferred Income	427,400		427,400		416,029
All other
Allowance for loan and lease losses:
Balance at beginning of period			2,437	$ 3,006	3,006
Total net charge-offs			639
Balance at end of period	2,314		2,314		2,437
Ending allowance on loans individually evaluated for impairment	0		0		0
All other | Non Covered Loans
Allowance for loan and lease losses:
Balance at beginning of period			2,437
Provision for loan and lease losses			516		183
Gross charge-offs			807		1,158
Recoveries			168		406
Total net charge-offs					752
Balance at end of period					2,437
Ending allowance on loans individually evaluated for impairment	0		0		0
Ending allowance on loans collectively evaluated for impairment	2,314		2,314		2,437
Loans and Leases:
Ending balance of loans individually evaluated for impairment	0		0		0
Ending balance of loans collectively evaluated for impairment	120,508		120,508		113,969
Loans and Leases Receivable, Net of Deferred Income	$ 120,508		$ 120,508		$ 113,969