GOODWILL AND OTHER INTANGIBLE ASSETS (Details) (USD $)					3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010	Mar. 31, 2012 Premiums on acquired deposits	Mar. 31, 2011 Premiums on acquired deposits	Dec. 31, 2011 Premiums on acquired deposits
GOODWILL AND OTHER INTANGIBLE ASSETS
Goodwill	$ 337,438,000	$ 337,438,000	$ 337,438,000
Market capitalization	3,490,000,000
Total stockholders' equity	2,283,297,000	2,311,743,000	2,157,917,000	2,113,931,000
Premiums on Acquired Deposits
Premiums on acquired deposits					115,200,000		117,600,000
Accumulated amortization for premiums on acquired deposits					50,900,000		50,400,000
Amortization expense of premiums on acquired deposits					2,900,000	3,200,000
Estimated Future Amortization Expense of Premiums on Acquired Deposits
Remainder of the year					8,033,000
Year Ending December 31, 2013					9,364,000
Year Ending December 31, 2014					8,454,000
Year Ending December 31, 2015					7,543,000
Year Ending December 31, 2016					6,634,000
Thereafter					24,289,000
Total					$ 64,317,000