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SECURITIES AVAILABLE FOR SALE, HELD TO MATURITY, AND OTHER - Summary of Securities Available for Sale and Held to Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	$ 1,426,400	$ 1,387,250
Available-for-sale debt securities, accumulated gross unrealized gain	4,139	7,108
Available-for-sale debt securities, accumulated gross unrealized loss	(29,140)	(13,444)
Available-for-sale securities, debt securities	1,401,399	1,380,914
Available-for-sale Equity Securities, Amortized Cost Basis [Abstract]
Available-for-sale equity securities, amortized cost basis	59,261	36,483
Available-for-sale equity securities, accumulated gross unrealized gain	0	9,211
Available-for-sale equity securities, accumulated gross unrealized loss	0	(509)
Available-for-sale securities, equity securities	59,261	45,185
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Available-for-sale securities, amortized cost basis	1,485,661	1,423,733
Available-for-sale securities, accumulated gross unrealized gain	4,139	16,319
Available-for-sale securities, accumulated gross unrealized loss	(29,140)	(13,953)
Available for sale securities	1,460,660	1,426,099
Securities held to maturity
Held to maturity, amortized cost basis	395,337	397,103
Held to maturity securities accumulated unrecognized holding gains	5,045	10,316
Held to maturity securities, accumulated unrecognized holding loss	(6,086)	(2,143)
Securities held to maturity, fair value	394,296	405,276
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Held to maturity and available for sale securities, amortized cost basis	1,880,998	1,820,836
Held to maturity and available for sale securities, gross unrealized gain	9,184	26,635
Held to maturity and available for sale securities, gross unrealized loss	(35,226)	(16,096)
Held to maturity and available for sale securities, fair value	1,854,956	1,831,375
Municipal bonds and obligations
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	112,857	113,427
Available-for-sale debt securities, accumulated gross unrealized gain	2,784	5,012
Available-for-sale debt securities, accumulated gross unrealized loss	(721)	(206)
Available-for-sale securities, debt securities	114,920	118,233
Securities held to maturity
Held to maturity, amortized cost basis	269,636	270,310
Held to maturity securities accumulated unrecognized holding gains	4,251	8,675
Held to maturity securities, accumulated unrecognized holding loss	(2,980)	(90)
Securities held to maturity, fair value	270,907	278,895
Agency collateralized mortgage obligations
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	932,723	859,705
Available-for-sale debt securities, accumulated gross unrealized gain	29	397
Available-for-sale debt securities, accumulated gross unrealized loss	(19,816)	(8,944)
Available-for-sale securities, debt securities	912,936	851,158
Securities held to maturity
Held to maturity, amortized cost basis	73,207	73,742
Held to maturity securities accumulated unrecognized holding gains	433	1,045
Held to maturity securities, accumulated unrecognized holding loss	(1,078)	(486)
Securities held to maturity, fair value	72,562	74,301
Agency mortgage-backed securities
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	195,526	218,926
Available-for-sale debt securities, accumulated gross unrealized gain	95	279
Available-for-sale debt securities, accumulated gross unrealized loss	(5,523)	(2,265)
Available-for-sale securities, debt securities	190,098	216,940
Securities held to maturity
Held to maturity, amortized cost basis	7,712	7,892
Held to maturity securities accumulated unrecognized holding gains	0	0
Held to maturity securities, accumulated unrecognized holding loss	(316)	(164)
Securities held to maturity, fair value	7,396	7,728
Agency commercial mortgage-backed securities
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	63,561	64,025
Available-for-sale debt securities, accumulated gross unrealized gain	0	41
Available-for-sale debt securities, accumulated gross unrealized loss	(3,003)	(1,761)
Available-for-sale securities, debt securities	60,558	62,305
Securities held to maturity
Held to maturity, amortized cost basis	10,465	10,481
Held to maturity securities accumulated unrecognized holding gains	0	0
Held to maturity securities, accumulated unrecognized holding loss	(509)	(268)
Securities held to maturity, fair value	9,956	10,213
Tax advantaged economic development bonds
Securities held to maturity
Held to maturity, amortized cost basis	33,996	34,357
Held to maturity securities accumulated unrecognized holding gains	361	596
Held to maturity securities, accumulated unrecognized holding loss	(1,203)	(1,135)
Securities held to maturity, fair value	33,154	33,818
Corporate bonds
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	100,963	110,076
Available-for-sale debt securities, accumulated gross unrealized gain	861	882
Available-for-sale debt securities, accumulated gross unrealized loss	(32)	(237)
Available-for-sale securities, debt securities	101,792	110,721
Trust preferred securities
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	11,297	11,334
Available-for-sale debt securities, accumulated gross unrealized gain	266	343
Available-for-sale debt securities, accumulated gross unrealized loss	0	0
Available-for-sale securities, debt securities	11,563	11,677
Other bonds and obligations
Available-for-sale Debt Securities, Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	9,473	9,757
Available-for-sale debt securities, accumulated gross unrealized gain	104	154
Available-for-sale debt securities, accumulated gross unrealized loss	(45)	(31)
Available-for-sale securities, debt securities	9,532	9,880
Securities held to maturity
Held to maturity, amortized cost basis	321	321
Held to maturity securities accumulated unrecognized holding gains	0	0
Held to maturity securities, accumulated unrecognized holding loss	0	0
Securities held to maturity, fair value	$ 321	$ 321

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