DEPOSITS (Deposit Liabilities) (Details) - USD ($)		Mar. 31, 2017	Dec. 31, 2016
Deposits:
Non-interest-bearing accounts		$ 3,213,044,000	$ 3,140,451,000
Interest-bearing checking		928,232,000	914,484,000
Regular savings accounts		1,592,023,000	1,523,391,000
Money market accounts		1,543,943,000	1,497,755,000
Total interest-bearing transaction and saving accounts		4,064,198,000	3,935,630,000
Certificates of deposit less than or equal to $250,000		992,896,000	884,403,000
Certificates of deposit greater than $250,000		151,822,000	160,930,000
Total certificates of deposit	[1]	1,144,718,000	1,045,333,000
Total deposits		8,421,960,000	8,121,414,000
Included in total deposits:
Public fund transaction and savings accounts		206,243,000	221,765,000
Public fund interest-bearing certificates		31,024,000	25,650,000
Total public deposits		237,267,000	247,415,000
Total brokered deposits		171,521,000	34,074,000
CD acquisition premium		$ 293,000	$ 426,000

[1] Certificates of deposit include $293,000 and $426,000 of acquisition premiums at March 31, 2017 and December 31, 2016, respectively.