BUSINESS COMBINATION (Details) (USD $)	12 Months Ended	0 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2014	Jan. 17, 2014 item	Jan. 17, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Business combination
Consideration transferred in the acquisition (in shares)	5,583,093
Issuance of 5,583,093 shares pursuant to MetroCorp acquisition	$ 190,830,000
Goodwill recorded as a result of the business combination	469,433,000			469,433,000	337,438,000	337,438,000
MetroCorp
Business combination
Number of branches		19
Number of subsidiaries		2
Percentage of purchase consideration satisfied in stock			66.67%
Percentage of purchase consideration satisfied in cash			33.33%
Fair value of the consideration transferred			291,400,000
Consideration transferred in the acquisition (in shares)			5,583,093
Issuance of 5,583,093 shares pursuant to MetroCorp acquisition			190,800,000
Consideration transferred in cash			89,400,000
Additional cash given to acquiree's stock option holders as part of consideration transferred			2,400,000
Amount given for warrant's assumed as part of consideration transferred			8,800,000
Goodwill recorded as a result of the business combination	132,000,000	121,000,000	121,000,000	132,000,000
Fair value of assets acquired		1,700,000,000	1,700,000,000
Cash and due from banks		230,300,000	230,300,000
Investment securities available for sale		64,300,000	64,300,000
FHLB stock		2,700,000	2,700,000
Loans receivable		1,190,000,000	1,190,000,000
Fixed assets		8,600,000	8,600,000
Premiums on deposits acquired		8,600,000	8,600,000
OREO		9,400,000	9,400,000
Bank owned life insurance		30,000,000	30,000,000
Deferred tax assets		13,000,000	13,000,000
Other assets		16,700,000	16,700,000
Fair value of liabilities acquired		1,410,000,000	1,410,000,000
Deposits		1,320,000,000	1,320,000,000
FHLB advances		10,000,000	10,000,000
Repurchase agreements		25,900,000	25,900,000
Junior subordinated debts		29,100,000	29,100,000
Other liabilities		22,700,000	22,700,000
Information relating to the acquisition of MetroCorp	11,000,000			11,000,000
Pro forma information
Net interest income and noninterest loss	1,028,796,000				934,207,000
Net income after tax	338,730,000				299,625,000
MetroCorp | Bank Owned Life Insurance
Business combination
Information relating to the acquisition of MetroCorp	700,000			700,000
MetroCorp | Additional Tax Adjustments
Business combination
Information relating to the acquisition of MetroCorp	$ 10,300,000			$ 10,300,000